Since our central heating system was upgraded in October we have noticed a singing noise in the house when the water circulating pump switches on. It is a new Grundfos UPS2 15-50/60 pump with 3 speeds. Reducing the speed reduces the noise but it doesn't go away, and we need to use the maximum speed to heat the house effectively.
The noise sounds like a musical tuning fork. It comes from any part of the house where there are pipes or radiators, as well as from the pump, but is not easy to pinpoint. It is not loud, just annoying. How loud it is depends on where you are in the room and what direction your head is turned. It is as though the noise from the pump transmits to the water everywhere in the system.
The system works well otherwise, there are no other clues, although there is a slight unrelated whistling from the boiler flue which is being investigated.
A Magnaclean filter was fitted and has removed about a cupful of black rust already.
Our plumber will be visiting and may try changing the pump but he seems stuck for ideas so I wondered if you could make a suggestion.