Have been down this road. Our 2008 Limited started doing the "ding ding ding" when reaching full open on the lift gate during this past winter. Basically what was happening, as I saw it, was that the actuator for the lift gate was trying to drive the lift gate past it's stop. It would actually make the lift gate bounce when it hit the top, and, thinking it hit an obstruction would go "ding ding ding". I can tell you from experience that sometimes it would not only ding 3 times, but sometimes would try to close again after it thought it hit an obstruction - with me still reaching inside. I could see the newspaper article... "Man Eaten by Edge"...
Anyways, took it to the dealer. Was definitely worse over the winter. They thought it was weak struts, so they replaced the struts. Still did it. So they ordered updated struts - still did it. I told them again what seemed to be happening was that the actuator wasn't stopping where it should, and no amount of struts is going to fix that.
Since the only thing left was the actuator, they replaced it. Bingo, now works as good as the day we bought our Edge. When I watch the new actuator, it stops about an inch before the lift gate reaches the top, and then lets the struts carry it the rest of the way, versus the old actuator, which tried to drive the lift gate right off it's hinges.
-S