well, honestly it could be a lot of things. but, if it is what i think you mean, it is the t-belt tensioner. they are called a grenade for a reason. they are a hydraulic tensioner, that after some time, the internal pressure seal gives up, and the tensioner kind of smacks itself. there is no immediate danger to the belt tossing off, unless the sounds really increases to very loud. the grenade should be replaced everytime the belt is. but they dont always last as long as the belt does. i hear ya on the nuisance factor.