Actually, there's one thing that puzzles me-perhaps you have an answer for this.
Given that the main drive sprocket is turning all the time whilst the chain is going round, why should it make more noise when coasting in gear than with clutch pulled in, or for that matter, when coasting out of gear (during which time that main sprocket is still in play)?
Haven't had the time to look at the sprocket to see if it's loose yet, but will over the weekend.