Regulators will "hum" (cause they don't know the words) occasionally and other than being annoying doesn't hurt anything. Its caused by rapid air movement thru the vent.
If you want it to stop just tweak the adjustment spring (tweak = move just a hair)
If that doesn't stop it replace it. I have had residential regulators moan like a train horn, that usually makes the neighbors happy.
Jim & Debbie England
Do you have Gas? 2015 F350 6.2L CCLB DRW 4.30 axle. 2012 Yellowstone Ridgeline 34RLT Fifth Wheel