Have you ever had any water in your engine?
Poss could be something in the ignitor/charging system area of engine.Or poss a one way bearing in the clutch housing.You can use a long screw driver and hold it up to your ear and place it in diff areas of engine to find area of noise.Good luck.
Thanks for the reply Bill appreciate it.No, I have not figured out what the sound is. It seems to be related to compression braking when in the higher gears. It does not sound like gears or a grind. It is a high pitch whine/scream sound.
Good luck with yours