Does the tub stay full all the time, like a hot tub? The reason I ask is that I have a hot tub, and once you get out and shut the jets down, it will go into a standby mode and hum while circulating and heating / filtering the water. It goes on and off about 15 minutes each to keep the water hot and filtered.
If you drain the tub after each use then disregard my comments.
If you drain the tub after each use then disregard my comments.