I started a thread about this a while back because I noticed a 6K resonance buzz. Since this post, I did the 600 mile service at the dealer and told him about the buzz. He said he rode it to check and it was completely normal. I think it is just an engine resonant frequency, assuming your symptoms are the same as mine. I'm at about 1600 miles now and I definitely don't notice it as much now. Don't know if it is perception or reality, but no worries. You're probably fine.
http://www.ninjette.org/forums/showthread.php?t=32225