Engine squeaking, please help

I have a noise under the hood that has been difficult to diagnose, and I have not found any threads with a solution. It is a squeaking sound coming from the front of the engine that gets worse when the car is warmed up. The noise changes with engine speed as well and seems to go away around 1500+ RPM (although it could be that I can't hear it due to the loud pipes).

To fix the problem I changed both idler pulleys and unfortunately the noise seems louder now. If I am hard on the car and run it up to redline the noise will subside, although it is still vaguely present. I think it has to be one of the other pulleys (alternator, power steering, coolant, or AC). The noise does not change when I turn the steering wheel, and does not change if I turn on the AC. Also, the serpentine belt seems to be in decent shape (changed around 25,000 miles ago). Any suggestions or similar experiences?

There are 2 idler pulleys on my 1998, one of them is attached to the tensioner, and the other one is attached directly to the engine cover. The tensioner is aluminum, but why would the tensioner cause the squeaking?

thanks Randy

Problem solved! I took the belt off again yesterday, and it appears there is nothing wrong with the tensioner (not bent, or causing the belt to sit unevenly). I then manually turned each of the accessories by hand, and noticed the alternator was making a slight squeak that was hardly noticeable unless you put your ear right up to it while turning the pulley. I then removed the alternator, and sprayed some white lithium lube behind the pulley, and on the rear part of the center shaft (I don't know the technical term is), and the squeak ceased.