My 1998 Gmc Sierra 1500 5.7l 350 has 109000 on it. The dealer I bought it from tells me the brakes have been done and it has new upper and lower intake gaskets. It is now making a loud screeching noise from the rear end. It get louder with the speed of the vehicle and when it has pressure going down hill. The noise definitely doesn't fluctuate with rpm. It gets worse with the speed of the vehicle and when it has pressure from accel/deceleration. Any ideas on what this problem may be. I placed the vehicle on jacks and put it in neutral to turn the wheels. They spin freely and silently. Doesn't seem to change with lane changes/hard or slight turns. Always the same sound no matter what direction. Leeds me to believe it is not the wheel bearings.