Triumph trident very loud knock at low rpm and not consistent?

[jh321]

The bike is a t150v triumph trident. I recently bought it and from what I can gather it has sat for a while (10 years). It has a loud knock/tap/rattle that is only when the bike is just kicked/fires and when the rpms are returning to zero/slowing down after being turned off. It will never happen when the bike is running at higher revs. I have tried listening through a screw driver to locate it but I can't pinpoint it.

The noise also will happen if I have the ignition off and just kick it. It has to be a very hard and long kick though.

Any thoughts on how to narrow this down? Would low octane gas cause a very loud knock or more of a high pitched ping?

 

[jh321]

After a bit of investigating it now seems that the noise doesn't happen at all when given throttle and running. Also, there is no slip point in the clutch and it snatches.
Could this be a sign? It seems it may be the clutch. What could be the knock?