A damaged serpentine belt can make a variety of strange and unexpected noises. The most common sound associated with a faulty serpentine belt is a squealing noise, usually heard when the engine is started or accelerated. This noise may be accompanied by vibrations, which are caused by the poor alignment of the pulley system that drives the belt. In some cases, this squeal may become louder as the vehicle accelerates and then quieten again at lower speeds. It's also possible to hear grinding or thumping noises coming from underneath your hood if you have an excessively worn-out belt. If these sounds persist it’s important to take your car in for repairs immediately as further damage could occur without prompt attention from a mechanic.