I have a 92 XR600R which has started to make a banging sound when the clutch is slipped. This typically happens when I'm starting off in deep sand. After about a second of slipping the clutch, I hear and feel a thud coming from somewhere down below. The condition and adjustment on the clutch cable, chain and sprockets are all okay. I did have one incident where the axle nut came loose and the chain slack increased to around 4 inches. I got the same noise then, but without the clutch being slipped. Mike.