Norcold Frige Vibrations

[stnick]

I just finished the install of my new Norcold frige DE0751. This is the replacement for the factory DE251. I had to enlarge the cutout by about a 1/4" on each side and other than that the install was straight forward. The unit cools extremely well. I am getting an annoying hum through the kithen sink and forward birth from the unit. It is not sitting on the hull. The only area toucning at all is the front mounting flanges where the unit screws in.
Anyone been here before and used some type of isolators or do I have a defective unit?

Thanks,
Nick