Please help with my car problem?

Okay, Ive changed the belt tensioner, the belt, and the harmonic balancer to my 1996 Cadillac deville and there is still a lound squeaky noise. It usually comes and goes, it will stop for awhile then start back up again. When it starts back up, the noise goes from low to loud. The noise usually only happens when the car is accelrating, but sometimes it squeaks very low when its just parked. Please help. What could it be?