That is a good question. Without making a recording of before and after it is hard to say but I tried, and then tried again, and then again.
We have a 3.6 cubic foot Norcold AC/DC refrigerator DE0041. It is much larger than the one we had in the Eurovan and does not need to be level like that one did. The Norcold normally runs off 12v and 110v when you plug into shore power. But, it is in many opinions noisy.
There is no way to stop the noise. It comes from the compressor which vibrates when cooling. The compressor is rubber mounted to reduce vibration transfer but the mounting does not eliminate it. There is also a fan but it makes almost no noise.
Peering under the refrigerator I saw a L-bracket that might have been touching one of the metal slides the refrigerator is mounted on. I wasn’t sure but that was good enough for me – I pulled the refrig out. It was actually easy and by the third time I did it real easy. Complete instructions are here, http://www.sportsmobileforum.com/viewtopic.php?f=13&t=487&hilit=dynamatting+the+fridge - thanks to jage and the Sportsmobile forum.
After I got it out I could see where the bracket might have been hitting . I got out the trusty Dremel, cut part of the bracket off, slid the unit back in, put it back together and turned it on . . . no change.
Out again and this time I tried those furniture sliders. Put a couple on each “leg” and slid it back in . . . no change, maybe worse. I think this is when I decided the best I would be able to do, is to mitigate the problem.
This time I added 1/8 rubber strips to cover the metal sliders. I used two on the right side to make sure it will finally line up with the cabinet. I used some silicon sealant to stick the rubber to the metal – just needed it to last while I put it back in. With the rubber you can no longer slide it, you have to “walk” it in a little at a time. With about 3 inches left to go you can tilt it up and adjust the rubber if needed.
Both the 12v and 110V wires were wrapped around the top of the compessor. I took those off the compressor to give it complete freedom. BTW, you also have to fish the drain tube into it’s hole when you put it back in place. I just used a piece of wire and when the refrig was almost in position, pulled the rubber hose though.
Is it quieter? Well, it has to be doesn’t it? I find out next week while on the road and it is time for sleeping.