Were your brakes pretty well worn? This truck has had new brakes 1800 mi. ago, but I have always noticed that they squeal a little the last 20-30' when I brake at a stop sign or light.
It's like this:
Put the Hummer in drive-runs like it always had.
Put the truck in reverse-runs like it always had.
Put the truck in reverse WITH the brakes applied, ie. not moving just sitting there stopped with gear selector in reverse and brakes applied=growling noise.
The trans mount seems to make a little sense to me in that if there was one that was toast putting it in reverse may cause the trans to shift under the torque load and come into contact with the frame or body, thus causing the noise. Once the brake is released torque is transferred through the driveline and growling stops.
