There are 3 things that make these pumps annoyingly loud IMO.
1. The hard pex piping on the pressure side of the pump vibrates against whatever it contacts. This could be the floor, walls or bulhkeads, etc. This can be defeated by changing the pressure line from the pump to the nearest fitting to flexible tubing, available at Lowes, etc. And also wrapping the hard pipe with foam pipe wrap wherever it contacts something.
2 The pump itself can transmit vibration even though it has a rubber base. My mod takes some of that vibration out of play. Mine was also mounted to the wall, not a good place IMO. It vibrated right through the wall to the master bedroom, LOUD.
3. Short cycling. Without an accumulator tank your pump will cycle on and off repeatedly when low water flow is being used (ie rinsing dishes). The accumulator causes your pump to cycle on and off less often so it is less annoying and easier on the pump. For small amounts of water the pump may not even come on at all.
For a quick noise reduction try # 1 first if you do not have the time to do the others, it should at least help. If the pump is defective of course it would need to be replaced. I believe mine is a Shurflo, as is the accumulator tank.
2004 Chevy 2500HD Crew Cab 6.0l, 4.10r
2010 Jayco Jayflight 28BHS
Reese Strait Line with Dual Cam
P3 Brk controller