Pikuoff

Rear diff replaced and the car sounds/feels new again. Will be sure to regularly replace the fluid from here on out! Unplugging the rear diff connector definitely helped while I was waiting to get it replaced for anyone in the same boat.

Rear diff is toast. The shop said all the sound was in from diff and coupler that's all one unit. It had lots of metal in the fluid. I tried to get most out with my pump but I guess that's why not much came out b/c my tube was pretty thin. About a $3k replacement. Probably not too surprising since it was never serviced for 170k miles. Now I know...

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.

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!!

Found the connector and disconnected it. Sound is gone.

Interesting. I will see if I can find it.

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.

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!

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?

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!

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?

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.

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?