I'm guessing it's a low speed thing, the UJ spider not running central to the driveshaft, but clears once up to speed - common with an older GS, not so often seen with an S10. Running the bike in gear on the centre stand is just about the worst treatment you can give the UJ, as others mention.
https://www.fowlersparts.co.uk/parts/5944980/xt1200z-super-tenere/drive-shaft - see part #45 & associated bearings.
I wouldn't be looking in the drive housing at this stage; just pull the driveshaft, examine the UJ bearings & hope they are just dry & need re-packing, if you are feeling very lucky.