I used to have an early 70s CB750 as a kid even that had a bit of whine at idle and it was never anything to worry about. Every YouTube video I have seen of a 919 at idle had the whine to some extent. Depending on where you have your idle adjusted you can almost tune the whine in to be more or less noticeable. At least thats been my experience. When I first got my 919 I was concerned about it as well but I suspect many other honda straight 4 street bikes have a bit of a whine. It also may not be very noticeable on bikes with full fairings.
I also love the whine. Just another sound to let you know you're on a 919.
'02 919 PCIII, Two Bros, Sargent, Ohlins, and some other stuff.