I have convinced myself to try the sound insulation project on my 88 Cat 30 this spring. I have researched and talked with the folks at soundown (www.soundown.com). I always thought it would make a difference, but like you how much of a difference, and was it worth the dollars and efforts. Looking at the statistical data, graphs does little to translate it to real world sound.....unitl I found the following link. They have a sound example of a uninsulated motor, and one with various brands of sound insulation. Pretty impressive... From reading all the technobabble, it is pretty hard to drown out 100 % of the low frequency diesel noises, but pretty easy to cut out the mid and upper frequency noises. It has to do with the size and construction of the material used and the ratings of the absorbortion layers vs deadening layers. Any way, come spring, I will give it a shot. I figure it has to help some and i budgeted the cost around $200-300 (Cnd $) for the soundown material.