I had the same problem, I think it is common on this ski. If you open the hood there are some bolts that hold the mirror assembly on each side of the ski. On my ski these were loose, and tightening them up significantly helped with the mirror shake, but didn't eliminate it completely. You have to be careful not to over-tighten, since the parts are plastic, and could break.
As to the hood itself, check the rubber seal. It may need to be replaced. I don't know whether you could make a gasket for it or not. Also look at the metal bar that engages the latch. It is covered with a rubber material to prevent it from sliding in the latch. Over time the rubber gets warn off or thinned out. I put a couple of rounds of electrical tape over this area to give the latch a tighter grip on the metal bar. This will keep the hood from sliding back and forth as much, but the latch itself is somewhat loose. I also put a thin piece of weather stripping material at the top edges where the hood sides touch the ski..........this is where mine rattled against the ski.
