I can’t believe all the above posters who say they are living with noisy pumps and don’t seem to have done anything about it!
We have a Salamander, probably the smallest available because we didn’t want to empty our rather small tank in one shower. The pump is attached to the pipework by four flexible hoses, which is a good first step in reducing noise. The first thing I did was to isolate it from the floor by standing it on something dense like a sheet of thick rubber on top of some sound-absorbing felt. After that I built a case to go over it made from plywood and chipboard lined with old carpet underlay; where there are pipes to fit around I cut long slots a couple of inches wide, the underlay bridges over inside the slot and has a cut running along so that you can slide the box around the pipe and the gap closes behind the pipe. Finally I cut some pieces of felt and packed them on top and around the outsides of the case.
It’s just a question of surrounding the pump with enough sound-absorbing material to soak up all the high frequencies.
The result? You can hardly hear the pump at all, just a faint hum coming from inside the airing cupboard.