Wow. That sure directly points at valve clearance as the source of the problem. I would find it very helpful to know if they removed and replaced the PAIR valve on the valve cover during the procedure. Just curious if disturbing the valve might cause grief.I just had my first service done. No rattle/clatter/bb,s in a can noise at higher rpm prior to service. Now I ve got the rattle!! Bloody hell! At first service they checked valves, they were off spec...so they used 3 shims.... Now I've inherited the dreaded rattle. (my invoice shows a charge for 3 shims, so aim assuming they used 3)
Also am curious to know if the valves were tight before the adjustment.
I had to change the two exhaust shims on my bike because the clearance was about .003" tight. However, I didn't notice any change in the bike's sound after the adjustment.
I hope you keep us updated and thanks for the post.