If your pump is a Surflo 2088-422 series; then they are inherently noisy.
Two things you might look at. Are your water lines to and from the pump hard plastic. My '01 Dip was hard plastic lines. Sureflo mounting instructions call for minimum 12" flexible lines on both intake and output sides of the pump. I inserted 14" steel braided water lines and that cut the noise in half. My prepump filter is clear and it has some air bubbles in it. Originally my filter was mounted on its side and had some bubbles. Now it is vertical. Still have some small bubbles. My lines are all tight, so I suspect that the design and construction contributes to a small amount of air retention.
Hpe this helps,
Roland, Diane & Katie - the furry 4-footed kid
'01 Diplomat - ISC330 - Allison MD3060 - Progressive Ind. EMS-50C - Hughes Autoformer - '06 Jeep Liberty CRD