The pulsating is too slow for it to be a tyre issue, it’s definitely related to a constant RPM more than the actual road speed
To be fair to Continental I loved them on my KTM Super Adventure just didn’t have the same results on the RTRE: Do you have Continental tires.
My bike's ridden poorly with Michelin PR4 and Metzeler 01 tires, but is as smooth as glass on the 4 sets of Continental Road Attack 3 tires I've gone through.
The issue could still be the tires, but I wouldn't start with "if they are brand X then they're fine" and move on to the next thing. If you think it might be tire related, get them checked out.
You don't mention the akrapovic exhaust. My K1300s got a weird buzz/hum at about 3700rpm that disappeared at 9500rpm. Very strange but I got used to it. The noise disappeared when I swapped back to the stock can. Now the RT, mines from June 2020, no top box and totally stock. 18900 km on clock andI’ve just got my very first BMW, a 2020 1250 RT and it’s driving me nuts. It’s brand new, now with 1,300 miles on the clock and at anything above a steady 3500rpm in 4th 5th or 6th gear it has a “pulsating” buzz which comes through the seat and you can also hear the hum hum hum (hard to explain) The Rev counter is steady, the speed is steady without and engine surging but it’s very obvious and mega annoying.
Has anyone experienced anything similar? Any suggestions as to what if May be? Should I be concerned?