well whenever i start up my truck my belt or a pully will screach, with the a/c off and lights off. now while in idle, if i turn my a/c on it will screach when i accelorate and whenever the a/c clutch kicks in. now after the a/c on and the truck in idle i turn the lights on and all hell breaks loose it will let out an almost continuous screach. anyone know what this is? i recently installed a used underdrive crank pully and alt. pully with a new gatorback belt.

 

How worn do they UD Pulley's look? I've heard that sometimes the aluminum gets worn down on those. Also, your belt tensioner could cause this.. best way would be to take the belt off and spin each pulley buy hand to see if you can replicate the squealing. My 2000 did this btw, I deemed the humidity to be the problem.

 

figured it out, my alt pully is off balance need to check that out this weekend!