I soundproofed the compartment the best I could with the dedicated sound material :
http://www.defender.com/product3.jsp?pa ... 5&id=95982For the aft end of the compartment, I built a removable plywood panel on which I added the insulation. All in all, it helped a fair amount, but sound still reverberates into the bilge and vibrations from the engine mount/fiberglass pan into the hull. Several things I plan on doing which will help: new engine mounts (vibration), adjust valve clearances (loud tapping noise, airborne), Add an air intake filter(reduce airborne noise) OR...................turn off the engine!!!
I have a W-40. I was told by a mechanic that I could attach a heavy walled hose of the appropriate diameter to the air intake and snake it through aft somewhere and this will greatly reduce the noise from the engine............haven't tried it yet but sounds interesting (no pun intended)