What could be causing this rattling? It sounds like a v-twin, happens only on acceleration. Isn't there on reving the engine with pulled clutch, and it doesn't happen on deceleration either. But give it a little gas (little or wot, don't matter), it is "arrrrrrrrrrrrrr", kinda like a vtwin. No loss in power.

What is it?

Bike is K3 Gixxer 1000 btw.