OK, here's one that's got me thinking!

My XT600E has started making a strange noise while running. It's a kind of slightly metallic sha-sha-sha sound (sorry for the crap description), similar to when you are passing regularly-spaced trees and the sound of the bike is reflected back at you. The sound is not unlike a loose washer vibrating. Fairly quiet, but just audible over the engine/exhaust at 40-60 mph. That's the best I can do! The puzzle is the frequency. At 40 mph, it happens at approximately 4 to the second, and varies with the bike's road speed. It is there with the clutch in and the engine dead, and carries on getting slower and slower until the bike stops. It's obviously chassis rather than engine.

The frequency is the puzzle. My maths (which could well be as rubbish as my descriptions) says that the wheels are turning at 8 (front) or 9 (rear) revolutions per second, which kind of rules them out, unless some strange feature is making the noise happen every second revolution.

My only answer is the chain, which at ~100 links with a 45T sprocket will make a full revolution at approximately half the rear wheel speed, or about 4 per second at 40. Does this make any sense at all?

It's n ot a big problem (yet) but I would like to put it right before it gets worse and starts wearing something important. Any comments or suggestions welcome. I should add that I have checked the bike over and nothing is obviously loose or rubbing.

Many thanks.

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2006 XT660R daily ride, 1994 XT600E about to be reborn, Blog: http://goingfastgettingnowhere.blogspot.com/