I would have to hear it to guess further but there is alot more going on in the right side of the motor, like the clutch basket and waterpump. I have heard waterpumps make pretty loud noises and they are easy to check and take apart.

You can run it without the one-way, I would also leave the 52t gear off since the one-way holds it in position. It probably wont bump start as easy without the one-way in or idle well, its part of the flyhwheel weight, so I would say 3rd gear down a good sized hill may do it.

 

Probably a long shot, but I had a similar rattle on two different occasions on my '01 Raptor. Once was the large gland nut on the front sprocket was loose. I guess I had not torqued it enough when I changed the gear even though the lock tab was in place. It would still move sideways on the spline. The other was found by raising the rear wheels and strarting it and putting it in gear. Turned out to be a bad bearing in the chain rollers. Both the upper and lower were bad but the upper had ball bearings falling out of it when I took it off. Once you ride in water, it takes a toll on these bearings. I replaced them both with bearing from my son's inline skates. They were a perfect fit and are sealed. It has been almost two years now. Hope this helps someone....

 

thanks for all of the replys