I hope this Youtube link works. First time I've tried it.

2008 RSV (triked) with 69,000 kilometres. Have a listen to the slight knocking sound that has developed in my engine. You can hear it clearly over the rumble of the mufflers, it's kind of like three rapid knocks together with a break and then three together and so on. The knock does not show up until the engine is warm (after a run on the highway), is most noticeable on the left side of the engine, does not change sound when the clutch lever is engaged and the engine oil is fresh and showing properly in the sight window. I just synced the carbs which made no difference to the knock. Obviously I can't hear the knock at highway speed but presumably it doesn't go away. Fuel mileage and performance has not changed at all since developing the knock. Otherwise, the engine is running as smoothly as it ever has.

Would appreciate some suggestions from you 2nd Gen experts as to what the cause might be.