Noises coming from the Heat Sipohn when it is off are usually rare but a few normal ones are
- a slight buzzing from the 24 volt transformer which should be almost imperceptable. If it is loud then it may indicate a problem.
- a hissing sound immediately after the unit shuts off which is the sound of refrigerant pressures equalizing through the thermoexpansion valve.
- bubbles from the pump wich indicates a suction line leak in your pool piping