They all make enough noise to scare a squirrel in to a mad dash.
Un-"shrouded" barrels on high power PCP guns have a little bark to them, though the shrouded ones, like the air foce talon ss, are a lot quieter when the power is set moderately. Just to see, I turned the power down from 650fps to 600fps on mine and all that is heard is basically the firing spring then a slight "psss." I had to bring the scope up a few clicks to get dead on at 50yds, but it was still flat out to there once zeroed.
Cabellas has a sale on the RWS 54 in .22cal going on. From what I under stand the "action" is floated and dampened for extremely mild recoil, thus a 100 dollar variable, with an adjustable objective, scope should live for quite some time, I like my BSA "Air Rifle" scope. That set up would provide plenty of power for rabbits and squirrels out to 75yds, with practice of course.