BF, do you have a go pro?
maybe hood mount it or get it somewhere outside to see if you can pick up a rattle outside. This sounds like a cab rattle to me but if you can feel it in the floorboards, and the harmonics match the rattle and it only happens while you’re moving it has to be related to the drive train. If it’s 2h / 4A consistent, I’d be inclined to look from the trans rearward. It almost sounds like a dying cat(alytic converter).
I’d suggest engaging a decent go pro externally to see if you can pick up a rattle with more audio clues. I’ve got one on my ZX10r that picks up a mysterious bodywork rattle on video, that is not in the audio sound track on the bike. It happens about 4-4.5k but I’ll be damned if I can track it down. I can only hear it on the GoPro !
Good luck with it.
