I posted the following in another forum and thought I would post it here too, cause I really need some help with this!

I need some help figuring out a problem I am having with my 13 GT vert,manual tranny, 3.31 rear end and brembo pkg.

I exited an apron at the firehall 3 days ago that is about a 10 to 15 degree incline on to a street that is about a 3 degree incline and I was at a 45 degree angle to both. I heard a clunk and then the rear end shimmied left to right.

The car has been doing the pop and shimmy since then when I accelerate at 3500 to 4500 rpm in 1st and 2nd gear, mainly, and I can get it to do it in 3rd also.

I removed the Left rear wheel and noticed a light rub mark on the upper inner fender well and on the inside rim of the wheel, but no other obvious issues.

Took it to the dealer and they straightened the main driveshaft guide bearing, which was loose and off centered on the drive shaft.
we also fixed a lock flange on the pass side LCA which had dropped near the sway bar, but no sign of rubbing.

That did not fix the issue, which is why I am seeking input from the Mustang experts on this forum.

Bear in mind the noise and shimmy do not occur under normal driving, unless the car is on a incline/hill where the weight is on the rear suspension.

Any thoughts ideas or experience with this type of problem?

Your help is greatly appreciated.