Alternator?

 

If you are sitting still in neutral and you rev the bike do you get this whine? If so rule out anything in the drive train ie belt or wheel bearings. If the whine is still there, the possible problem is one very well known to HD and it's reputation for cheap *** parts... I would definitely check out the cam shaft bearing and/or bushing.

 

Yes, my bike has the whirring noise when sitting still and if I rev the engine, I get the spinning sound in the engine bay.

 

Sounds like a loose drive belt to me...check your belt tension.

A loose drive belt will whirl and whine on deceleration, almost sounds like a turbine.

 

Like I said... rule out the drive line, belt, wheel bearing, etc. if it is whining while sitting still. None of those parts are moving... could be cam bearing(quite common in Harleys... could be primary chain... could be stator.

 

I had that happen after having a rear tire replaced and after inspecting the indys work found the drive belt as tight as a piano string. Adjusted the belt to spec and no more noise.