Drive belts and pulleys wear evenly with use. Unusual signs of wear indicate some correction is needed. The following diagnostic chart will aid in diagnosing multiple ribbed belt system problems.
Chirpings : Chirping is a high pitched noise that is usually heard once per revolution of a pulley or belt. It is also usually heard at idle and is most common on cold damp mornings. By squirting water onto a chirping belt, the noise will momentarily go away.
Squeal: Squeal is a loud screeching noise that is usually caused by a slipping belt. The noise usually occurs when a heavy load is applied to the belt, such as compressor engagement, accelerating the engine, or the belt slipping on seized pulley.
Whine: Whine is a high pitched continuous noise that may be caused by a failed bearing.
Rumbling: Faint cyclic rumbling is a deep low frequency noise (once per revolution of the belt).
Pilling: Pilling is the random accumulation of rubber dust in the bottom of the multi-ribbed belt grooves. A small amount of pilling is normal. Operation of the drive belt system will not be affected unless buildup exceeds 1/3 of the belt groove depth.