Thanks Roy. Pieces of foam, carpet, pipes tied to one another or to something else - I've been through all of this. It is quiet-er now, not quiet enough for me. Sometimes it's resonating in odd places like plastic bathroom sink 10 ft away starts rumbling. Quality of these carton boxes on wheels doesn't seize to amaze me.
Short On-Off intermittent bursts when you open the faucet just a little, are the worst. Very crude pressure sensing in Shurflo.
Have been eyeing this
Shower Booster - it "sounds" like a quiet but the cost is prohibitive. I understand this is an on-demand pump, 2A current, they don't tell PSI. Ignore the AC power supply, the pump itself is 12V.