Growling decelerating in overdrive?
 

First off, car specs:
1991 Mustang LX 5.0 (engine is bone stock, for now).
4.10 rear end.
AOD trans.
SVE upper and lower control arms.
KYB rear shocks.

So I installed a 4.10 rear end from another mustang, and now about 65mph (or 2100RPM) and up I get this really loud growling coming from under the car. It ONLY happens in overdrive and ONLY above 2100rpm. I can be in 1st, 2nd, 3rd, doesn't matter, it's nice and quiet until I drop it into overdrive. I did A LOT of testing last night to ensure it only happened in overdrive above 2100rpm. It overpowers my radio even when I got it turned up. I didn't want to use your guys time trying to solve this problem, but I literally couldn't find a single case like mine ANYWHERE.

However, here is the kicker! Me (and the guy I bought the rear end from) drove the car this rear end came out of and it was whisper quiet in ALL gears at ALL speeds! However, it did come out of a car with a T5 tranny in it.

I don't see a 'edit' option, so I apologize for the double post, but it also stops and goes quiet once it hits right about 2050rpm. No idea why.

If the u-joints check out good, and your tranny didn't do this before. Are you using your original driveshaft or did you swap that too? Just curious as I thought the AOD and T5 driveshafts are different lengths.

And I think there's a write up on here somewhere on setting pinion angle. Just thinking off the top of my head here.

Thanks for the reply! It's the stock driveshaft, and I will check the u-joints. I have no idea if it was doing it before, as I had the 2.73's and to get up over 2100rpm would be like roughly 120mph. I couldn't go that fast because my old rims were bent so bad the car felt like it was going to shake apart. I got new rims and the rear end at the same time.