I apologize in advance if this gets long but I need to explain the circumstances in which I hear this sound. I seem to only hear it in 3rd gear and above but it could be happening in the lower gears as well - I just may not be able to hear it. As I'm cruising and if I snap the throttle back quickly, I hear it. It doesn't happen all the time as I'm guessing it depends on my RPMs. The sound is as if you take a very thick braided cable and stretch it until it breaks. The initial snapping sound of when it first breaks is the sound I hear. I noticed it the other day while riding with a bud. He could also hear it while on his bike. However, today while on the highway coming home from work I could hear it while just cruising but not as loud as if I were to crack the throttle. It didn't come up often, maybe a few times within several miles while on the highway. However, it's obviously getting worse since before today it only happened when I snapped the throttle back. Any ideas??? Oh, the sound only lasts for a split second. Another analogy of the sound would be a short hissing sound from a blast of air.

 

Very difficult to diagnose a sound. But I'll throw out maybe a spark plug has backed out some? Or something loose in your air cleaner?

 

I have the same bike and from your description what you are hearing is the lash in the drive train or the ratchet on the auto tensioner is not latching correctly and allowing the chain to hit some part of the primary. Driveline sounds like a snap when clearance is taken up, (normal) but the primary tensioner sounds more like a hiss or click. It's hard to diagnose some of these sounds over the internet since your description and mine will be different. It could even be the ip bearing making the noise, but if throttle imputs were the start of it, which has an effect on chain tension, the adjuster would be what I'd look at first.
Ron