When I start up my '01 GTP I've been hearing a squeaky noise coming from the left side of the engine bay where all the belts and pulleys seem to be.

Unfortunately, I'm not much of a technical genius in cars to figure out which pulley is loose or what not. My dad is taking a look at the car too and he thinks its an idler/tensioner pulley or something along the lines of that. His Chevy Venture had a pulley that crapped out so he thinks that's whats going on based on his hunch.

My car is stock so if I have to replace a pulley, is it worth to buy another stock one or actually attempt to get one that would upgrade the car's performance? I've heard that doing pulley swaps if not done in the right order could put strain on the tranny.