I have a 99 Tahoe 4x4 5.7l The tensioner pulley has been sqealling for some time. Ive just been spraying it with lubricant. I finally decided to change it. I swapped out the pulley and it sounded great. About ten minutes later the new pulley started sqealling. I sprayed it with lubricant to very that and sure enough that is the problem. So the question is what would cause this. Oh yea I replaced that pulley about a year ago as well. Do I have an alignment problem? Why would it begin to sqeall again so quikly?
Often it's the muck that's sprayed on that is causing the problem, belt grip is the worst of all. Remove the belt and clean or fit a new one, clean all the pulleys with solvent, check bearings of idler and tensioner pulleys, and re fit. Alignment should not be a problem as miss alignment will destroy a belt long before a pulley will fail. There are laser aligners out there to check these things, but that a bit much for the home mechanic to worry about.