2020 Rebel 500, about 65,000 km (40k miles). I weigh 100 kg (220 lb).
The problem: I feel a steady, rhythmic bump through the seat while riding. The beat gets faster as I speed up, and it's still there when I coast in neutral, so it's not the engine. I feel it on smooth asphalt too, not just on concrete with joints. It gets worse when I lower the rear preload (I'm on 4 now).
What's been done so far:
New Michelin front tyre (the old one was damaged; the previous owner rode it underinflated)
Both wheels taken off and balanced. The rear needed extra weights. The mechanic spun both on the machine and checked the bearings, all looked fine.
New chain and sprockets (the bumps were there before this)
Pressures 29 psi front, 30 rear
Also: at 100 km/h in 6th, hands off under engine braking, the bars wobble slightly side to side and settle at lower speed. Much better since the new front tyre, but still there. Nothing felt with hands on the bars.
My mechanic thinks it's just the basic stock shocks, but a beat that tracks road speed and continues in neutral makes me think something is rotating.
Next I plan to try a few extra psi in the rear (in case the rear tyre is damaged inside like the front was), check for disc rub, and put tape on each tyre to see which wheel lines up with the beat.
Has anyone had this on a Rebel? What did it turn out to be: rear tyre, discs, cush drive, or something else?