Shifting problem

04 Honda Rubicon 500. Wont shift properly. Will go into gear on the screen and shift with buttons but it seems like the transmission isn't fully engaging. As I start to rev it up, its grinding and then finally lunges forward. While making a ton of noise. If i come off the throttle it sounds like it drops into gear but then as soon as I try to throttle it again it sounds like pops out of gear and grinds until it lunges forward.