Possibly a belt idler or tensioner pulley? Had similar happen to me, and then one day on a local street I heard POW, CLANK, CLUNK, and felt someting hit the floorboards and I was like ? Pulled over and found the blower belt layen on top of the snout, and the idler pulley completely gone, and as JAmie on MYTHBUSTERS would say: "Well, theres your problem"!