Rep Power: 0

I have an 03 DX manual. so the car starts up fine and seems to run fine. But two weeks ago noticed when i accelerate passed 4000rpms i hear a whinning/whistle noise (honestly it almost sounds like a turbo). But it goes away as soon as i let go of the gas (even though I'm coasting and the revs are +5000rpms). Any Ideas or thoughts.
Recent repairs/work on the car:
-Changed belts in summer of 2009
-Front breaks rebuilt summer 2009
-AC installed summer 2008
-Input shaft bearings were replaced summer of 2007.
-Rear break converstion summer 2007.

Don't know if that it of history may help or not.

Thanks