Scraping/Grinding Noise

Heres the issue. If my car is slightly heavy- (full tank of gas/passenger, etc), I will hear a scraping/grinding noise from the back of the car somewhere. It is difficult to locate while driving, but it is somewhere around the driveshaft/rear end. It will only make the sound while under acceleration. If I drive gingerly and accelerate slowly as to not let the rear suspension take a load, the sound wont happen. Once the car is at a constant speed, the sound stops.

The car is a 94 GT 5.0l, 5-speed. This problem is seeming to get worse, and I cant for the life of me figure out what it is. I cant make the sound happen when its at a stand still, on jacks. Any ideas?

Turns out it was the e-brake bracket. The rear part of the bracket, which looks to be spot welded onto the body is ripped from the metal it was welded to. It is being pulled/bent down by the tension of the brake cable, so that it is about 1/2" from the driveshaft. I can clearly see where it is grinding. Should be as simple as moving the driveshaft out of the way, bending the bracket back up, and welding it back to the body. Thanks all.