Noise, eyewitness opinion from an expert is really all I need. The Gamo Urban is claimed to be mouse fart quiet and it is. It should be quiet, it has modest power and an engineered LDC.
Dont need no stinking decibel meter!
How to tell if a rifle is going to be pretty quiet:
177s are the quietest.
22s aren't bad.
25 use more air and make more noise.
Is it high powered for its caliber? It will make more noise. Fer-instance, the Urban only makes about 22fpe whereas many 22cal rilfes make30-35fpe, because the urban makes less power it will be relatively quiet when compared to other 22s.
Has the manufacture installed a quieting system such as a shroud or mod? If so this gun should be pretty quiet.
Unshroud Korean high powered rifles are loud as are their ilk, like AirForce heavy hitters.
Expert eyewitness opinion: What does Steve say? Or Matt?
FX rifles like Streamline: They have a modest shroud and these bark a bit on high power, however, on the medium and low settings they are very quiet.
Carbine sized rifles, like a S510 carbine have a short shroud that helps but it still barks on high, turn the knob down a bit for quieter operation, this is what I do when the Clauger is in the drawer. It's very quiet with the clauger.
Word of mouth from other hobbyist.`
Airguns are going to make a bit of noise, make sure you are using them in sensible ways in accordance with the rules.
I'm not around mice much and have never heard one fart, I assuming it makes a quiet noise when farting. My kids a cat that farts, but I've haven't heard that either, but it reportedly stinks.