2000 GMC Sonoma Serp. Belt will not stop chirping

About 2 months ago I noticed some cracking in my serp. Belt. Replaced the belt and the auto tensioner, tensioner because felt it may be due. Ever since I have had problems with the belt chirping. I took the tensioner back and got another replacement, no help. Got another belt, good for a week then back. Cleaned all the pulleys with brake cleaner and brush, put another new belt, new tensioner and new idler pulley. Good for a week then back again. It does it at idle while cold, but goes away at idle after warming up. Always does it while driving. I have used the same brand of belt and tensioners, Dayco. I even tried the more expensive poly cog, I believe thats correct, belt. I noticed that if you get the smooth side of the belt wet right at the idler pulley it goes away for a few seconds. I sprayed belt dressing on the smooth side of the belt and was good for about 3 days, but then the sound came back. I think it is slipping at the idler pulley, but I have done and replaced every thing I can think of. I even wrapped electrical tape sticky side up around the idler pulley just to see if that was where the slip was and the sound was gone. Obviously not a fix as the tape lasts all of about 10 seconds. Could it be a load of defective belts? In total it has been 3 tensioners (old one included), 5 belts, 1 idler pulley (not counting original one) and multiple headaches.