We had the same issue on our boat
, trouble is it is mounted onto a bulkhead so noise
will resonate through the boat
. I improved ours by installing some soft rubber motor
mounts between the pump/accumulator assembly and the bulkhead, this made a reasonable improvement. Also check the air pressure in your accumulator tank, I found ours had a small hole in it and would loose pressure, causing I replaced it with a bigger size one made by Grundfoss and it works even better now.
The other thing you could do is relocate the pump to the bilge area, still mount it on a rubber mounts.
We have dry bilges normally, if they are wet then this becomes a priority #1 for us, if you have wet bilges is it salt
or fresh water?
Recently we had a number of freshwater leaks
, whilst plugged into the marina, I found out that the water pressure at the marina had somehow been increased, we found a few hoses leaking, also strainer cap cracked. Anyway I have adjusted out feed pressure valve and re secured the leaking hoses all good not.