LP gas noises

I recently had my two 30 pound LP tanks filled on my 5th wheel. Since then whenever my refrigerator is operating on gas I can hear a chirping/whistling noise coming from one of the tanks outside. If I switch the auto valve to the other tank the noise stops. I checked to make sure the tank hand valve was fully open and that the hose connection was tight and there are no leaks.
Any ideas what the chirping noise is ?