When I get up to highway speeds ..... 117 or above the engine will intermittently kick into a rough sounding and feel. If I adjust the throttle a little it goes away and the engine levels out and is smooth. It however will come as I said intermittently. Is this normal.
That's about the speed where some owners notice a belt vibration.
If it won't go away with a belt tension adjustment, you might need a belt vibration damper.
Or you can just avoid that exact speed where it occurs.
I have the same thing happen around 75-80 Mph it's the belt vibration that causes the noise. It's not a problem and will not hurt the machine. Sometimes I just speed up and it goes away other times I slow down 2 or 3 mph and it stops.
It won't hurt the bike but it is very annoying. I had a tensioner put on but that was of no help. I had the front end rebuilt and still it was there. What I found was running the front tires with 20 pounds of air helped. I believe it's in the tires. They are not made very well so its my opinion that is the problem. I have a 2016 RTS with 45000 miles on it. The bike is very well maintained but the problem is still there.
And you have not changed the tires.......why exactly ??
If you still have the stock Kenda's, you should love the difference if you change to a different brand.
OH......and don't ignore the rear tire as a possible cause.