That is odd, mine turns stayed quiet between 22:00 and 06:30 all winter. My programmable thermostat sets back to 18C at night. During the day it cycles on and off, after ramping up to 21C in 3 steps during the morning.

If you are outside you can hear a quiet hum if you are close enough, but only when it is pumping. It is in my front yard and I can't hear it in my back yard on the other side of the house. I see that my neighbours have them, but can't tell when theirs are pumping by listening.

The sound of air coming from the HVAC ducts is louder than the outside unit sound in most of my house.