Just a quick update from my side. Video of my engine tappy/rattling/clonking whatever you wanna call it is here :
http://bit.ly/7V0jw
Original reported to SBW in Hertford, possible noisy waterpump was the response
Then took to Vines in Guildford which is about 60 miles away, engine is hot so the noise is less noticeable, sounds normal was the response
Took the bike to my "local" dealer, Battersea, London which was the most helpful so far would you believe it ... Veronika organized for it to be booked in and a loan bike (another 800GS which btw, sounds completely different to mine). Left the bike overnight, as the sound is at it's worse when cold and the next morning I quickly had the "normal" response until I opened the throttle slightly at which point the technician was like, Ohhhh, yeah !
First response, a coil ??? misfire ??? I find that hard to believe ! I then said, " well, can we get it fixed" and his response was, "Depends how deep your pocket is"

Warranty job mate ...
They then kept the bike, put it through diags which apparently flagged up nothing, but they replaced the coil and there was some problems with the spark plugs as well according to the job sheet. At first it sounded ok (not 100%), but much better .... until this morning, the noise is back again
Going in again next week and I think I am going to bug them constantly until this engine is fixed and/or replaced ... will keep you updated.