On my new 2018 RTL I had 3 distinct and different vibrations.
The engine makes a resonance that I feel in the bars, kind of a mild buzz. It may be intake or exhaust resonance, but I consider this normal as it is a fairly high horsepower engine. The engine vibration is stronger with application of throttle.
My belt came way too tight from the dealer, and made a nasty buzz around 70-72 MPH. I lowered the tension of the belt and reduced the speed of the belt vibration to around 50 MPH, but it also softened the vibration harshness. Kind of like plucking a guitar string, looser is lower pitch or something like that. This vibration was more load dependent, occurring on hills or accelerating through the speed it happens at, felt throughout the machine. I installed a Doc Humphreys belt dampener and it almost completely eliminated this vibration, so much so that I can't tell if any is left.
My third vibration came from the tires. One of the OEM Kenda tires wouldn't balance, so I replaced them with suitable car tires. I balanced them myself with a Marc Parnes balance shaft, which doesn't address dynamic balance, only static. While the bike runs pretty darn smooth right now, I've installed the Centramatic wheel balancers, which should finish off the tiny bit of tire shimmy I am experiencing. This vibration can be speed dependent, getting worse in a range of speed. When I had the Kenda imbalance it made the fenders shake and the handlebars shake more than vibrate. The tires don't actually go around that fast, and you can use the frequency of the vibration to kind of pinpoint where it is coming from.