The serpentine belt tensioner can fail; it may become noisy and/or the belt may jump off. Replacement of the failed tensioner will be necessary.Google+
Car Problem Reports
GMC Sonoma Serpentine Belt Tensioner May Fail
GMC Sonoma Problem
Engines Affected: 2.2L 4 Cylinder, 4.3L V6
Average Mileage: 105,000 mi (55,000 mi - 150,000 mi)
Mine squeaks but only during summer when I use the AC. Water from some where is getting on the tensioner which then starts squaking. I change the AC setting for less cool air and the squeak eventually goes away.
Visitor, 2002 GMC Sonoma, 4.3L V6, 150,000 mi
Belt tensioner is about to fail. Chatter on the belt caused the bearings in the Alternator to fail. There is one more pully that is making noise when the truck is in gear, moving I can hear that there is vibration. Other people outside the vehicle hear it too.
The transmission contacts had build up on them, the vehicle now has 160K and will be needing a new tranny.
I am the original owner, it has been a good truck.
Visitor, 1998 GMC Sonoma, 4.3L V6, 55,000 mi
Belt tensinerwore out anf fell off!