Hi,
Just a thought, I had a 2002 XJ600 which developed a tapping noise from the engine, found out it was caused by a weak spring on the cam chain adjuster shoe. On the front of the engine between cylinders 2 & 3 you will find a hexagon headed stud behind which is the spring, When I had the problem the mechanic removed this stud & pushed a thin steel bar into the hole to increase the tension on the spring, this stopped the noise, the cure - a new spring.
The noise on my bike occured all the time though, but might be worth investigating.
Regards
Bri