Air source heat pumps are only about as noisy as a standard household fridge. And considering they will be installed outside the home, the low level of noise they produce whilst in operation shouldn’t be of any concern at all.
In actual fact, air source heat pumps are actually quieter than other household appliances such as washing machines, and actually emit a slightly lower sound output than traditional gas boilers as well.
For further information, take a look at our blogs, Busting The Myths About Air Source Heat Pumps, and our Ultimate Guide To Air Source Heat Pumps, and this air source heat pump guide from the Energy Saving Trust.