schrill whine from engine

[Old71Rider]

I have a 1999 standard with 45K. Several time while stopped with the engine running and the bike in neutral I've heard a high pitched whine, almost like a whistle sound coming from the engine.
Engaging the clutch with sometimes stop the noise. Other times it continues with the clutch engaged.
Any ideas of the cause of this issue?

[Farside]

 You should post this experience and question on the 1500 tech board. You'd most likely get several suggestions and faster response too. 

[OLDFRT]

Check your Instant Messages.  i (Old Fart) sent you Wood Butcher's Cell #. With his Permission.