Ive got an 88 2.8L Camaro and just last week got the water pump replaced in it. Ever since I got the new pump put in the belt (or so I think it is) is squeaking pretty bad. At first it started squeaking to a very minimal and eventually slowed and stopped at the engine ran more. So my first though was the berring in one of the pulleys is going out...so I replaced this with the same result. This morning however I tried to fix the problem by touching a wax candle to the belt as it rotated...This kept it quiet for about 2 minutes so I though it was fixed...WRONG. As I drove down the road the wax must have worn off and it now squeaks Insanely bad and is ear piercing. My dad thinks that the new water pump is bigger and is pushing the edge of the belt to the side of one of the pulleys. This theory would make sense because it started just after the pump was replaced. If tried using WD-40 and Gun Oil on the belt which also temporarily stop the squeak but attract dirt/dust and doesn't last long. If any of you have some product that I could apply to stop the squeaking or a permanent solution PLEASE let me know! this car is nearly undrivable because of this issue!

 

Check to see if the belt tensioner arrow is within the scale on the top of the tensioner. Also check the belt for cracks. If the belt is severely cracked or the tensioner is adjusted outside the scale, the belt needs to be replaced due to stretch.

 

Often that means the belt needs changed, the rubber isn't grippy anymore, long as the tensioner works right.

 

Similar to what your dad said, the water pump might not be longer, but it's pulley might not be seated on the water pump's hub correctly either, causing misalignment everywhere. Use a long straight-edge to make sure all of the pulleys are square to each other.

And I agree, usually, new water pump = new belt, especially if the old belt got coolant on it.