Check out this insulation from McMaster Carr:
I just installed it in my motor box and was on the lake today for the first time with it. I used the 1 inch skinned self-adhesive stuff. Time will tell how the adhesive holds but it sure is quiet. I can hear the exhaust rumble better now.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, Acme 1285, PPass, rear 750 sacs, KGB, IBS
(previous) 2001 X5, 1991 TriStar 190