I have a Kymco Agility R16+ (2021), I have the same problem and noise. All Identical!
On my scooter I have checked and tightened all visible bolts (kickstand, body, etc), replaced the variator (whit malossi), belt, clutch and bell! The noise is still there! I don't hear it when it's on the stand, stationary! (at least I think so). I was thinking a problem with the exhaust, manifold area (gasket/bolts) or internal (some internal broken part!).
When we are sitting on the scooter our weight probably affects the position of the exhaust.(
)
The scooter is perfect in performance. Just this noise on acceleration. I follow this discussion. You are the only one with the exact same problem as me!
I was looking for information on this and found this post!
I forgot... I have already change motor oil, trasmission oil and spark plug!