Are heat pumps noisy?

An air-to-water heat pump should not create a lot of noise, if it is operating normally and is correctly installed and maintained.
An air-to-water heat pump has an outdoor unit that contains a compressor which produces the heat for your home. As it operates, it will make some noise. On average, this is between 40 and 60 decibels (dB) which will depend on the size of the heat pump.
For comparison, the Alpha Heating Innovation E-Tec Plus combi boiler range has a sound level between 52dB and 55dB. A normal conversation at 1m away is around 60dB; a modern domestic fridge freezer operates between 40dB to 45dB.