In case anyone is still interested in the noise problem, its been resolved. I removed the head off the left cylinder and found the reason that one had soft carbon on the top of the piston. That is the side that has the crankcase pressure relief valve that allows the oil to be reburned. I cleaned it and decarbonized the head and put it back together. Then on a slow ride at around 3000 rpm the clacking noise returned. I bent over to try and hear it a little better and then I saw the horn shaking wildly. That was the noise! Once I removed the broken horn, problem solved! Wish I would have checked that first and save me all the trouble. Live and learn.