Could this be the buzz bolt? (I had it on one Valk)
http://www.valkyrieriders.com/shoptalk/buzz.htm
It is not where he's pointing, it's a bolt through a long sleeve inside the frame (at his knuckle). The nut gets loose enough, it lets the sleeve inside the frame rattle or buzz (mine rattled). Usually on throttle, not on coast, and may or may not have onset at a certain RPM and above. It's really the sleeve rattling, not the bolt. It drove me crazy.
I had to really crank on it hard, hard enough I thought I might break the nut/bolt (it squealed). I think I actually had to pull/bend the frame members it runs through together a bit to capture the sleeve. It's tool steel and didn't break.
It's harder on the interstate, because the bolt is inside the right pod. Accessible through the side vent, with a ratchet, extension and Ujoint (and if you slip, you can break the pod easily). Or take it off. Working alone, you can't reach to hold a tool on both sides, but I was able to tighten down from the right only, the bolt didn't turn.
Some pulled it apart and squirted the sleeve full of RTV sealant and reassembled.
The Shoptalk says some drilled/tapped a hole in the sleeve for a set screw. I never heard of anyone who did that, though it would work.
The origin of Valk sounds is often not where you suspect.
