Depending on the model of frig, you likely have a fan mounted behind the frig accessible from the outside vent. Mine was screwed directly to the metal on the rear of the frig and caused a lot of metallic vibration, sounded like a high pitch squeal. I remounted it (and 2 more) onto a small piece of wood then attached the wood to the metal frig. Hardly noticeable now. Good luck. I can send you pic if you like.
2013 Rockwood 8282WS
Reese Revolution Pin, Reese 16K
2008 Tundra Limited Double Cab 5.7L
Air Lift 5000 w/Wireless Air