i have had nothing but problems with the bed on my rtv 900. as for the rest of the machine, its awesome. i use mine to haul a lot of firewood and the two sides always seem to bend out a little bit when i dump off and then the tailgate wouldn't close. so i would have to tweek the two sides by pushing them towards each ather and then they would be at the right position for the tailgate to latch. over time of doing this, i noticed the little angle iron at the bottom rear of both side panels was cracking. so out comes the welder. after still more problems with it, i ended up welding the side panels to the bed floor, both inside and outside. problem solved. back to your issue, as i played around with the two side panels, i also noticed the vibration you spoke of and if i tweeked the side panels towards each other just right, the tailgate would fit tighter and no more vibration. this is where i put mine before welding the two side panels. no more vibration.