Bad Vibration

Well I was riding and after I landed a jump my rear end started shaking. It felt like the chain came off so I pulled over and seen it was still on. But as I revved the bike it still shook. Im in neutral and it feels like the swingarm is shaking so I thought maybe an engine mount broke. Well I dont think that is it. Also it was really hard to put it in first. I had to stomp on the shifter to get it to engage. So I'm thinking it might be in the transmission? idk the inside of the engine to well but could it be the counter balance or crank?

what is this on?

A Honda trx450r.
I already dropped the bike off at my mechanics so it shoul get worked out. He thinks its in the transmission but we will find out for sure soon.

Give us an update when you find out what the problem is. We like to know possible weak points.