Quiet is a relative term...what's "quiet" to an old, half deaf guy like me is one thing, "quiet" to a 3 year old is quite another matter.
My 22 and 25 cal PCP guns are "quiet" to me and also most of the game I shoot...my 177 RWS 48 is LOUD and my 177 Umarex Octane is louder than my PCP's and not as loud as my springer. ANY velo over about 1000-1200 fs depending on your altitude will have the "speed of sound" noise. It is very apparent in my Octane with light pellets but not with the lower velo heavier ones.
Go to the Air gun forums/links like Pyramyd, Air Gun Depot, Air guns of Arizona and/or the others and ask them...some have ratings included in the descriptions that might give you an idea.
Luck
