A couple of possibilities - the last one may be of the most interest if the damper unit is a possible problem (I have not had the ST apart enough to check the damper unit at the front of the shaft) (all of this from the now archived
www.my-mc.com) (note to Diesel - may be worth saving some of this while we are still collecting relevant information - I have saved a lot of this sort of information over the years , some of which is still readily accessible, some not):
Another possibility: (Service Manual item number)
The (20) Clutch outer (clutch basket) has slots that contact the tabs on (14) clutch frictions. If there are wear notches in the basket, the friction plates can hang and then release, causing a clunk. This would happen at mild or heavy throttle. This has not a problem for me, but had glazed frictions (slipping clutch) 40K miles ago.
If this occurs only at a heavy throttle, it could be something else, there is a primary damper deep in the engine, but have not heard of a problem in there.
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the primary shaft is the diagnosis that Martin reached ages ago. There was a recent thread with a picture of it somewhere...It has a cam that is spring loaded, and so is meant to give at times to protect things.
My 1100 would do this clutch chattering thing, usually during warm up before everything is fully up to temperature. I also noticed it was more frequent directly following an oil change. At 150,000 miles the problem developed to the point where it was doing it hot or cold and slipping at the same time. Fresh friction plates and springs solved it for the 15,000 miles or so that I rode it after that before it was sold.
I'm not sure what causes it but it was much worse with certain oils in the sump. Motul coming to mind as the worst one. My theory is weak clutch springs allowing the chatter.
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One thing I have not seen mentioned here is the possibility of the noise coming from the damper unit on the front of the drive shaft. Last year I had a loud snapping noise when I let out on the clutch. It was very infrequent and would only do it when the bike was rolling. I checked everything from motor mounts to the rear end. I needed to grease the swingarm bearings anyhow, so I pulled the swingarm and driveshaft out and disassembled the front damper unit. I found the seal had failed, all of the gear lube that was supposed to be in there was long gone and everything was dry and starting to rust.
There is a collar behind the seal that was coming into contact with one end of the driveshaft/damper and scored pretty bad. This was causing the one part of the damper unit to hang up, then let go, causing the snap noise.
I bought a new seal and collar, cleaned everything up and reassembled it. It now works very smooth and doesn't make noise at all.
