Hundred bucks says that's your starter failing. One of the failure modes for them is the return spring for the drive gear breaks and lets it contact the flywheel intermittently - especially when either accelerating or decelerating. I would pull that starter out and have a look. Remove negative battery cable. Pull the fender liner on that side, remove the exhaust manifold heat shield, remove the 2 bolts holding the starter on from the bottom, remove the power cables to the starter, and pull it out. It'll take you 20 minutes, including jacking up the front wheel and supporting the frame on a safety stand. If that spring is bad the drive gear will drop down to the end of the shaft when you hold that end down, or at least be very easy to move down the shaft. Had the same sound on my '07 (no AFM) and it was the starter.