94 potiac gran prix noise problem-help

I've been searching for a noise problem on my GP for about a week now. You hear it when the engine is running and sound like a "whine". It varies with engine speed. You hear it as you go up thru the gears from 1st to 4th but can't hear it at highway speeds or at above 40 MPH. I took the belt off and turned everything I could by hand and there was no bearing noise and they all turned freely. I even replaced the belt but no good. I suspect the belt tensioner but could not put any tension on the roller when I turned it. The tranny was overhauled 2 years ago and has been fine since. The car has 150000 miles on it and I know; get rid of it, but its good looking and runs great and also no payments needed. Any ideas what it might be? Thanks to all who give an opinion.