Over the last about 48-72 driving hours I noticed a clunking sound when decelerating. It is in time with the front sprocket. Now it is radical noise when slowing down and when coming to a stop it's a fast clunk then slows. I was thinking oh great after all the money I sunk in this pit the transmission is gonna blow up. In the driveway, in neutral (no engine running) I can roll it fwd and rev and there is a loud "clunk clunk" as it moves. This leads me to think it may not be the transmission but something else.

I did have the front pulley off last year to replace the GBPS sensor, it was fine with no red dust or cracked/broken grooves. Put it back together with a fresh bolt from cheapcycleparts.com, torqued to the higher spec. It shifts & accelerates smooth as butter. The clunking doesn't come to the back tire (no jerkiness) when it is slowing down.

I am clearing out a space in the garage to jack it up and take the belt off to start with rocking the front pulley to see if there is a lot of play, then take it off. Looking at the drive system on cheapcycleparts (clutch plates out to front sprocket) I don't see what could wear down and and make a gap or something.

It may be my imagination but I swear I hear same noise on all GS/RS on when it's moving, but it really quiet. Maybe whatever "moves" or has a gap just cracked or broke. Clutch basket maybe?

I imagine some gear head has seen (rather heard!) this before and might know what it is I am praying!!