It is (virtually) silent.Having a three way fridge fitted in my conversion by Cambee. Looked at all options and the biggest tick in the box which made us opt for three way was a simple one - three way is near silent when running on gas according to them.
And as my wife is exceptionally noise intolerant, there was no way a noisy fridge a few feet from her head was going to be getting her vote. And since a noisy fridge would also going to lead to a noisy wife, it got my vote as well!
I can hear the gas burning if it is quiet, and at night when REALLY quiet I can hear (presumably) the liquid circulating on 240v, but it is incredibly low, Mrs CAB can't hear it, and as it is constant it isn't disturbing