Westernstar w/C15 Loud in Cab

maybe put some dynamat on the dog house

 

I was in the same fix, fighting that low "rumbling" noise in my '04 W900. Did two things that helped, planning on more mods in near future. First was to glue some 1" neoprene sponge to the lower part of the firewall that angles away from the engine and meets the floorboard, (upper section has factory insulation). I also glued the sponge to the underneath of the floor, above the tranny. For what it is worth, the sponge is attached from the outside, in the engine compartment, and as I mentioned, above the tranny.

Last weekend, I had taken both door panels off to work on the window "roll em up and down gizmos". After putting a little grease on the friction points, (The little power window motor thanked me for that!); two coats of undercoating were then applied to the inner doors, and the inner door panels. I actually thought this would be a wasted effort, figuring the large padded door panel would do the sound dampening in that area. Pleasant surprise Monday morning when I noticed the difference. Think I am going to spray the undercoating on the underside of the cab, and sleeper floor, where I couldn't glue the sponge.

 

Dynamat or Lizardskin, the latter is a ceramic type product, I think you can roll or spray it. They use both in sound competition, so should do a world of good. I'd also look VERY close to be sure no clamps are touching the floor anyplace.