One of the first mods I made, see thread
here. Scroll down a little there are a lot of pictures on that thread.
The hoses attached the pump do the most to quiet the pump...they absorb the shock of the pump pulses so the hard pex piping doesn't bang against the walls.
I bought my accumulator tank online but you can find them at Lowe's cheaper than the PPL link above. The tank just plumbs into the pump output line with a Tee fitting and stores a volume of pressurized water to maintain pressure in the water system without the pump running. So the pump doesn't run every time you flush or open a faucet. I can use a fair amount of water before the pump turns on, then it runs for a while to rebuild pressure in the tank. If you install one be sure to put a valve ahead of it so you can bypass it for winterizing.