Inboard pumps are not noisy by design, they are noisy due to air being drawn in with the water and or poor installation? My own for the record originally sounded like a machine gun on steroids!!
Main problem is air inside the pump chamber, this first lowers the efficiency of the pump and the noise that makes is amplified by the air space rather than damped if the chamber was fully filled with water.
Simple check if air is present in the water exiting the pump, then this should be visible as you can see the water moving through the pipe, it's not water moving you see but micro bubbles of air trapped in the water, if no air then you can't see clear water moving
Air can get in via a poor connection outside of the aquaroll pipe, but, also the semi rigid pipe connections are designed to prevent water leaking out, NOT air being sucked in?!
Also ach 90deg elbow joint adds the equivalent of 2ft to the total length of pipe, the overall resistance this causes again makes the pump work harder sucking in the water, inturn increasing the air being drawn into the pump via the joints. All this fairly hard pipe can also vibrate and if it's touching walls etc, then makes even more noise!
So very simple answer to all that is replace with a single length of soft hose.
In my case I then rested my Whale pump which itself is mounted on a fairly large board to accommodate valves etc on a piece of breathable ground sheet. it is then fully insulated from the floor which would otherwise act as a sound board further increasing any noise the pump does produce.
Result is near silence and totally inaudible over the low volume of the TV , having done much the same to his and on hearing mine, Metz on here reckons his Truma pump is even quieter!!