This is a repost from this past weekend. I did not get any responses and am reposting in hopes of getting some hits this time:
I've got a 'whirring' sound coming from my rear primary area. I had one of my local HD mechanics ride it, he adjusted the cam chain and said everything is cool. The adjustment didn't take care of the noise though. It's not loud, just faint, and only makes the noise when the clutch is engaged. If I disengage it the noise immediately goes away. Any insight?

 

I had the same thing and it was my compensator nut backing off. Check that out, first.