I have a 2005 Ford Expedition 2WD and there was a vibrating/chattering sound coming from the rear end at take off when turning left or right. Based on some web research, it related to the limited slip rear differential. I called a few shops and let them know what was going on and they went directly to dropping the rear end, replacing the parts, etc… a $ 1K plus job. Luckily I found Fearless Gear. I explained the situation to Alec and because the sound only came from take off, he didn’t think the differential needed to be replaced and a simple service with some additives would do the trick. After the service, the sound was gone almost immediately and he said it would get better and better as the additives worked their way into the gears. If you need differential work, these are the guys!