If the rattle is rpm specific, itās most likely in the engine or parts directly connected to the engine. If itās speed specific, then itās in the drivetrain.
An issue pretty much all Polaris have is the drive shafts are welded with the U-joints out of phase. While the shaft angles arenāt enough hard enough to make it a major problem, there are some so far out of phase that itās noticeable.
One Xpedition I worked on had a bad vibration at around 32 mph. The front shaft was around 48Ā° out of phase and the splines are keyed. I had to grind the spline out so that I could get it close, but it was still a half spline off from being in phase. Even after doing that, it still had the vibration at 32 mph. This time I pulled the driveshaft completely out so we could look at it and the front shaft had about a 3/8ā bow to it. Rather than just getting a new shaft from Polaris and chancing the same issue, we had a driveline shop replace the shaft tube and they made sure it was welded together in phase.
Because of that bowed driveshaft, the front differential bearings were bad and that had to be replaced.
As Iāve said before, Polarisā quality control leaves a lot to be desired.