1999 1500 silverado 4x4. when driving with the fan on i get an intermitten squelling like a belt slipping. it only happens over 1500 rpm. if i drive under 1500 rpm it does not make noise and if i turn the fan control off while driving over 1500 rpm it stops. any idea's?
truck has 130000 mi on it.

 

Are you running the defroster? This would automaticly turn the AC on putting more load on the belt.

 

• sounds like it may be the water pump bearings

 

How old is the serpentine belt? Check the belt and the idler and tensioner. It sounds like the belt might have stretched some and starting to slip at times which will get worse as time goes by.