[jambo]

Some important questions (to my mind at least):

1) How long have you owned the bike?
2) Is this a new noise?
3) When does it occur? Is it apparent at idle, higher rpm, constant throttle, closed throttle, opening throttle etc?
4) Is the bike particularly high mileage / what it it's rough history?
5) Has there been any other recent work to the bike (including servicing)?

Without this we can make some guesses, but there's no point having you chase some thing around the bike's recently had a traumatic event for instance.

Jambo