Having experienced idler gear bushing explosion on my '05 SM I would describe the sound afterward as the starter spinning easily w/ no connection to the engine. When it occurred, there was a sound like a small firecracker going off near my ear - I thought it was the bushing exploding but it may have been a backfire which apparently can cause the dastardly event! If your problem is undiagnosed, you can drain the oil, then remove the clutch cover on the left side and the damage will be obvious if this is the problem. The good news is TR covered the repairs out of warranty since this is an obvious manufacturing defect - my bike had only 7200 miles on it at the time! They will change the crankcase so it shouldn't happen again.
