Whine/Roar when AWD is engaged

[Pikuoff]

I have a 2015 SEL with 170k miles.  Lately, I've been hearing a whine or roar that sounds like it's coming from the middle/rear of the car.  I've narrowed it down to only happening when AWD is active.  I used the dash AWD display and whenever the meter shows power to the rear wheels, the sound occurs.  When all the power is at the front, I hear nothing.  As it transitions to all power to the front, you definitely hear the sound just stop like a lightswitch turned it off.  As soon as power goes to the rear, you can hear it turn on again.  I was thinking PTU since those are so bad in Fords, from what I've read, but since the sound is more to the back and turns on/off, would that be the rear diff?  Do you think it is cooked or just needs a fluid change?  Haven't driven through deep water and haven't done much towing.  Any other thoughts or ideas on what to check?

[STBEAST]

Sounds like PTU but could be either one. Sometimes sounds can travel (shafts, couplers etc.) making it sound like it's coming from a different area. 

From all the reading on PTU's I would think that to be the issue. Since it is whining but still engaging, there is a chance changing the fluid could be the case. 

I wouldn't drive it until you can get the fluids changes in both units.

Hopefully, you get lucky, and a fluid change fixes it. 

Someone else will respond who knows more than I do about this issue.

[1004ron]

53 minutes ago, Pikuoff said:

I was thinking PTU since those are so bad in Fords, from what I've read

With that said, have you been changing fluids on the PTU? - if so, what interval and what oil?

[Pikuoff]

7 minutes ago, 1004ron said:

With that said, have you been changing fluids on the PTU? - if so, what interval and what oil?

I have not been.  It was never recommended to me by the dealer back when we went there regularly.  I didn't know what a PTU was until this popped up.  This was my first AWD vehicle so I'm learning quite a bit as I diagnose this sound.  I was reading a post along my searches that the PTU is always spinning so I figured if that was the case, then the sound would be constant.  My initial thought when the sound began was rear wheel bearings.  Even went as far as ordering some new ones (they were replaced around 60k by the dealer).  However, that's when I noticed that it wasn't making the sound all of the time and the ride was still smooth.  That led me down the rabbit hole of the PTU.  Was going to replace the fluid in that but then saw info about it being potentially the rear diff instead.  I guess I might as well do both while down there.  Just wanted to see if anyone had other opinions or things to look at based on the description.

[1004ron]

At a 170K miles and never had the PTU fluid changed, I'd be leaning towards that being the source of the noise.

 

It's probably not recoverable but would do a fluid change on it first - the fluid, if there's any left, will give you a good indication of the PTU's condition.

I expect yours doesn't have a drain plug so will need an oil extractor - when you replace it be sure to add a drain plug - a search of the forum will provide details on how that's done.

[Pikuoff]

5 minutes ago, 1004ron said:

At a 170K miles and never had the PTU fluid changed, I'd be leaning towards that being the source of the noise.

 

It's probably not recoverable but would do a fluid change on it first - the fluid, if there's any left, will give you a good indication of the PTU's condition.

I expect yours doesn't have a drain plug so will need an oil extractor - when you replace it be sure to add a drain plug - a search of the forum will provide details on how that's done.

yea, I was going to crawl under and see if it does have the drain plug b/c I've see mixed responses here and other places on whether the 2015 does or does not have it.  I guess I'll replace the fluid in both and hope that gets rid of the noise.  I'd be curious to see if the PTU can be bypassed altogether to make it solely FWD?  Has there been any experience with that?

[Pikuoff]

Whelp, got the fluids changed in the rear diff and PTU.  No change in the noise, unfortunately.  My PTU does have a drain, which was handy.  Guess I'll take it to the shop and see what they come up with.  Ugh...

 

Thanks for the info and recommendations!

[1004ron]

My 2017 Sport has a slight whine but haven't identified the source and my PTU and RDU fluids look good.

 

I haven't heard of widespread failures of the RDU but  Cerberus below report is one.

 

 

[Cerberus]

2 hours ago, 1004ron said:

My 2017 Sport has a slight whine but haven't identified the source and my PTU and RDU fluids look good.

 

I haven't heard of widespread failures of the RDU but  Cerberus below report is one.

 

 

To be fair,  I should give you more of the story.

At about 65k miles I brought my edge to the dealership for the brake hose recall. While it was there I asked them to look at a couple other things including a bearing noise from the rear of the vehicle. Had a warranty that was running out so I wanted to use up whatever I could of it.

They claimed they could not duplicate it. When I got under the vehicle to check / change the RDU fluid next it was about 8 months later, and the RDU was EMPTY. 

Now anyone can figure out that there's no way it could have gone 65k empty, and there are no leaks, so they pimped it out hoping it would grenade so they would get the job. 

I ended up doing the rear wheel bearings and that fixed the noise at that time, and ive kept changing the fluid and cleaning the magnet on the fill plug, but I took a 2k mile road trip last month and I've noticed new noise from the rear,  different than before,, and with all the metal flake that's come off the plug, it's not surprising that it's on its way out 

But my point is, this is a one-off situation that bears no resemblance to normal use with even minimal maintenance  

[Pikuoff]

1 hour ago, Cerberus said:

To be fair,  I should give you more of the story.

At about 65k miles I brought my edge to the dealership for the brake hose recall. While it was there I asked them to look at a couple other things including a bearing noise from the rear of the vehicle. Had a warranty that was running out so I wanted to use up whatever I could of it.

They claimed they could not duplicate it. When I got under the vehicle to check / change the RDU fluid next it was about 8 months later, and the RDU was EMPTY. 

Now anyone can figure out that there's no way it could have gone 65k empty, and there are no leaks, so they pimped it out hoping it would grenade so they would get the job. 

I ended up doing the rear wheel bearings and that fixed the noise at that time, and ive kept changing the fluid and cleaning the magnet on the fill plug, but I took a 2k mile road trip last month and I've noticed new noise from the rear,  different than before,, and with all the metal flake that's come off the plug, it's not surprising that it's on its way out 

But my point is, this is a one-off situation that bears no resemblance to normal use with even minimal maintenance  

Thanks for the info!  Was your noise only when the power would transfer to the rear for AWD?  I initially thought my noise was rear wheel bearings but then noticed it only occurred when power transferred to the rear.  I assume the noise would be all the time if it was the bearings, right?

[Cerberus]

2 hours ago, Pikuoff said:

Thanks for the info!  Was your noise only when the power would transfer to the rear for AWD?  I initially thought my noise was rear wheel bearings but then noticed it only occurred when power transferred to the rear.  I assume the noise would be all the time if it was the bearings, right?

The wheel bearing noise in my case was most evident after one particular turn on the way home. the long sweeping turn loaded the bearing in such a way that it made it complain and make more noise.

 

The new noise now happens when i lean into the loud pedal, which would definitely make the RDU clutch ramp in and deliver more drive force to the rear end, so yes, the noise is most audible when power transfer to the rear in active

[Cerberus]

one more thing to consider is that the center bearing on the driveshaft could be on its way out, and that would certainly be an easier & cheaper fix than the RDU.

that would roar. the RDU would certainly be capable of making a roar / whine combination noise too.

 

Edited July 22 by Cerberus

[Cerberus]

On 7/17/2024 at 1:13 PM, Pikuoff said:

yea, I was going to crawl under and see if it does have the drain plug b/c I've see mixed responses here and other places on whether the 2015 does or does not have it.  I guess I'll replace the fluid in both and hope that gets rid of the noise.  I'd be curious to see if the PTU can be bypassed altogether to make it solely FWD?  Has there been any experience with that?

the PTU bolts to the right side output of the transaxle between the output splined socket and the (shorter) CV shaft that sends power to the right front wheel. .

if you wanted to make it FWD only, you could do so by just dropping the driveshaft out.

You could also remove the RDU if you really want to, but it may be unnecessary unless it grenades on you..

 or go all the way and also remove the PTU and install the longer CV shaft from a FWD model.

This last option is likely unnecessary unless the PTU is confirmed as a source of impending failure noises

Lots of options

Edited July 22 by Cerberus

[WWWPerfA_ZN0W]

whine or roar from the rear part of the awd system is not a good thing. you will likely end up replacing the rdu if it has gotten to this point.

 

maybe its just the tires, but statistically, it will turn out to be the rdu. check fluid level and condition first. see if refreshing the fluid helps any. it is $$$ without warranty to fix a failing rdu.

[Pikuoff]

14 hours ago, WWWPerfA_ZN0W said:

whine or roar from the rear part of the awd system is not a good thing. you will likely end up replacing the rdu if it has gotten to this point.

 

maybe its just the tires, but statistically, it will turn out to be the rdu. check fluid level and condition first. see if refreshing the fluid helps any. it is $$$ without warranty to fix a failing rdu.

I don't think it's the tires since it isn't a constant whine.  It's only when power goes to the rear to activate AWD.  I did replace the RDU fluid and the sound is the same.  Figured it would be pricey since the fluid change didn't help...bummer.  Thanks for the info!

[Cerberus]

2 hours ago, Pikuoff said:

I don't think it's the tires since it isn't a constant whine.  It's only when power goes to the rear to activate AWD.  I did replace the RDU fluid and the sound is the same.  Figured it would be pricey since the fluid change didn't help...bummer.  Thanks for the info!

Just a thought, but it occurred to me to disconnect the electrical connector at the RDU to prevent the computer from having the clutch ramp in. This should minimize wear if you have to drive it.

[omar302]

3 hours ago, Pikuoff said:

I don't think it's the tires since it isn't a constant whine.  It's only when power goes to the rear to activate AWD.  I did replace the RDU fluid and the sound is the same.  Figured it would be pricey since the fluid change didn't help...bummer.  Thanks for the info!

 

I had a recent issue in an MKS where it had a whine coming from the back that I was confident was a wheel bearing. A mechanic had suggested that it was from the tires, hence I rotated the tires front/rear and the sound switched to the front. New tires fixed the issue.

[Pikuoff]

1 hour ago, omar302 said:

 

I had a recent issue in an MKS where it had a whine coming from the back that I was confident was a wheel bearing. A mechanic had suggested that it was from the tires, hence I rotated the tires front/rear and the sound switched to the front. New tires fixed the issue.

Was your whine all the time or just when AWD would kick in?  As soon as mine turns off AWD and all power is at the front, the sound goes away. 

[Pikuoff]

2 hours ago, Cerberus said:

Just a thought, but it occurred to me to disconnect the electrical connector at the RDU to prevent the computer from having the clutch ramp in. This should minimize wear if you have to drive it.

Interesting.  I will see if I can find it.

[omar302]

9 hours ago, Pikuoff said:

Was your whine all the time or just when AWD would kick in?  As soon as mine turns off AWD and all power is at the front, the sound goes away. 

 

Probably was most of time, hence my thinking it was a wheel bearing. 

[Pikuoff]

21 hours ago, Cerberus said:

Just a thought, but it occurred to me to disconnect the electrical connector at the RDU to prevent the computer from having the clutch ramp in. This should minimize wear if you have to drive it.

Found the connector and disconnected it.  Sound is gone.

[Cerberus]

9 minutes ago, Pikuoff said:

Found the connector and disconnected it.  Sound is gone.

I mean, it's not a fix for the problem per se, but it should greatly slow the deterioration of the RDU into a RUD (SpaceX shorthand for rapid unscheduled disassembly) 

[Pikuoff]

53 minutes ago, Cerberus said:

I mean, it's not a fix for the problem per se, but it should greatly slow the deterioration of the RDU into a RUD (SpaceX shorthand for rapid unscheduled disassembly) 

Haha, I know...just wanted to be able to drive it until I can find the time to take it to a shop.  I appreciate the help!!

[Cerberus]

On 7/25/2024 at 10:31 AM, Pikuoff said:

Haha, I know...just wanted to be able to drive it until I can find the time to take it to a shop.  I appreciate the help!!

So I went ahead and unplugged mine this morning, just to reduce the urgency of the swap.

Surprising how much quieter it is now lol

[Pikuoff]

21 hours ago, Cerberus said:

So I went ahead and unplugged mine this morning, just to reduce the urgency of the swap.

Surprising how much quieter it is now lol

Agreed!  I have an appt at a local shop this week to see what is actually failing.  The tech I spoke to had familiarity with this issue and had some good feedback on what he was going to look at.  Will report back once I know more.