Update.... since Lefty had the same problem...( even though his sig pic looks like he doesnt have one)... The buzzing turned out to be the "showchrome" fender rail on the front. Turns out one of the fender bolts came loose enuf to cause a small gap between the fender and rail, causing the " metal to metal " buzz at a certain rpm
just for a second or two. Probably did it in every gear as I shifted, but couldnt hear it til' I was coasting into driveways and parking lots with no throttle.