I go along with the others.....the only buzzing sounds I ever get are from something loose......Turc explained the Pivot Arm adjustment perfectly and that's probably the main culprit for a buzz.....just a little slop.
The other place I've seen a buzz come from is that aluminum insert that is under the screw which tightens the hook arm to the Pivot arm.....crank that down good and snug.

ALso check your set screw contact plate....it's just sort of floating up there and could come loose pretty easily if not tightened properly.

And the moleskin is a great idea for the hook arm.......not for the buzz, but for quieting the draw. DEAD SILENT. Don't pick a really thick material.....the stuff with just a bit of loft is good.
cut two traingular strips.......one for one side of the "V" and one for the other. They should just meet at the bottom of the "V"(where the arrow rests during the shot) and form a smooth seam together.
Very sweet.
Mine is as quiet as quiet gets......no buzzing clanking banging whatever, so something is DEFINITELY not adjusted quite right.

IF you need anything else feel free to e-mail me.