Ok so it can be one of 2 things from the top of my head. One is what happened to me was the idler pulley bearings went bad and it did sound like i was supercharged lol. Other worst case scenario is the rear end. However go with the cheapest and easiest which is replace idler pulley
1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.