Modern Vespa

Vespa GT60 has developed an vexing buzzing noise. Low RPM, slow speed.
The buzz seems to be coming from under and back. Only happens when rolling and can not be reproduced on the center stand.

Sounds metallic kind of like a catalytic converter rattle on a car.

Tapped, banged and shook all parts but can not be reproduced when standing still.

Things I have tried - tightened all screws and bolts, removed license plate and holder, removed crash bars, muffled the spring from center stand, padded marker lights and rear light. Looked around and wiggled things in the engine compartment but can't see where anything there would cause the buzz.
This one has really got me stumped.
Is it possible that a failing carbon muffler packing is causing the buzz?
I tightened the clamp with no effect.
Looking for an "a-ha" moment with somebody saying "Yes, had the same thing, it's the xxxxxx!"
Thanks forum - feel free to comment zzzzzzzzzzzzZZZZZZZzzzzzz

Could it be the stand tapping against the floor?

I dont know what kind of muffler you have , but could it be the heat shield, or maybe something in the muffler coming loose ?

Thanks for the suggestions. Sadly, it is none of those. I will start removing trim bits. Also replace muffler packing. More later.

Removed and inspected muffler, variator, clutch, transmission cover, springs holding center stand, all trim and lights removed from body. Yikes.

This is driving me crazy. Or maybe I am already crazy.

Even used a selfie stick and video/audio while riding but got nothing so far.
Will revisit that process with hope that a clue as to where this is coming from.

Carb? Engine? Loose weld on body. Seems to be coming from the lower engine area. AAAAAHHHGGG!

PS - when looking at the belt it was worn on the "teeth". Rubbing against the idler pully? Causing buzz? Will get a new belt too.

Idler Pully rolls smooth but does have a little bearing play.