I have an 87 mustang. So little over a month ago I had a set of rear gears installed. When i got the car back the shop said there was a slight whistle when decelerating/coasting. Now I've had a couple people tell me that's normal. And when I first got the car back if i remember correctly the car felt pretty smooth on the highway. And over time the car started shaking on the highway at first over 80 and anything over 85 started to shake from the back end real bad, and the shaking has been getting progressively worse.Now i did the five lug conversion before getting the rear gears installed. And i replaced wheel bearings all four corners. I've got my wheels rebalanced and got an alignment. I brought the car to another shop to see what he thought about it. He rode in the car and drove it. And with the combination of the whine and the shaking. He thinks it's something to do with the rear end for sure more specifically with the pinion and the it may have lost preload. If any one thinks this is the case, would I be able to tighten up the preload myself with only removing the driveshaft and tightening the pinion nut?