I have replaced the water pump about 3,000 miles ago and just replaced the belt tensioner pulley assembly because the pulley had some play in the bearing and was making some noise; however, I'm still getting this squealing noise at idle after it is warmed up. If I rev the engine it will go away and then come back once the engine is at Idle. I'm thinking the water pump is making this noise what do you guys think? Alternator pulley spins freely and bearing is smooth and quiet with belt off.

 

The spring tensioner can get weak. Just a possiblility.