Peculiar 'chuffing' noise.

[nick crisp]

This has been going on for some time now, but damned if I can pinpoint it  :\  The bike rides perfectly, and I have covered several thousand miles with it doing this. It's almost like a sawing noise, heard at lower speeds. It speeds up as the bike does, and I thought it might be pads rubbing on the discs, but it doesn't seem to speed up enough to be that, and I can see no evidence for it - discs are fine, brakes work fine. Plenty of material left on the pads. No evidence of anything rubbing on the tyres that I can see. Only does it when accelerating at these lower speeds (say 10-40mph approx), doesn't do it with throttle off. The chain has been adjusted a couple of times since I first heard it, made no difference, neither did a thorough service, which also didn't turn up any problems. It seems quite loud too.


Anyone got any clues what it might be, what to check?