I have a 1999 Alero and I have replaced the following components on the serpentine area and I still have a squeak. I replaced the power steering pump, alternator, upper and lower idler pulleys, belt tensioner and 3 different brands of serpentine belt. I STILL HAVE A SQUEAK after the engine reaches 2000 RPM. I am at a loss of what to check next.... HELP

 

It could be a bad bearing on the idler pulley, water pump, AC compressor, alternator, or just an old drive belt.

 

Check all the pulleys to be sure they are in line. Its a difficult thing to do at times, but you can get a good idea by looking down the belt. Also check the harmonic balancer to see if the outer ring has seperated from the inner, sometimes the rubber will let loose and the pulley will move slightly.