There are many ways to quieten the pump, depends on what is causing it. Often it is the plywood surface it is sitting on. Try putting 2" thick piece of closed-cell foam under the pump. Length and diameter of intake hose matters - the shorter and wider, the better.
My Flojet 03526 wasn't quiet. Shurflo Revolution 4008 was better.
They all make noise. Only once I saw a quiet one:
12V Inline Centrifugal Pump. Could barely hear a sound in the video. The guy tried it in the US market, went to Dragons, - big mistake :). I used to watch this show sometimes, then lost interest. Episodes are heavily edited, questions and answers are cut and mismatched to make it more exciting. Main question they always ask - How much have you made in sales already. If the number isn't big enough they are not interested. Boring.