I have a similar rhythmic vibration, like running over rough pavement, more noticable the faster you go. 3 little bumps then nothing, then 3 bumps again..
have 3 thousand miles and this is Just now happening. I think its something wrong inside my rear tire, maybe. Last ride , during a break, found a piece of metal sticking in tire. Kind of flat. Bout 3mm wide. Pulled it out slow looking for leak. Penetrated 12mm. No leak. Vibration started about 80 miles later, before I got home. Maybe coincidence , maybe cord was damaged. Have appointment with dealer. Will update.