Can't give you a direct answer, Dan, but how about a comparative one :-)? I have an older AA S400E .177. That's the older bolt action, full power, fully shrouded model. This thing is quiet enough that the first time I shot it, I thought something was wrong. At the time, I still had my Talon SS with 18" .22 barrel. MUCH louder! That was part of the reason I let the Talon go. I'd say it's at least as quiet as a good springer. And the newer ones have a larger shroud that's supposed to have a better baffling system, in short, it's supposed to be even quieter than mine.
If you're looking for truly mouse fart quiet, look at the FX T12 Whisper. I haven't shot one, but I've heard reports that it's about the quietest production PCP available. Price is about the same as a new AA 410 ERB. BTW, I consider the FX and AA guns very comparable, I also have a .177 Cyclone. They're both great rifles, I truly wouldn't say one is better than the other, just different. Power levels are about the same, I think you'd be happy with either one.
Both have outstanding triggers, incredible accuracy, and excellent fit and finish. The AA is a very classic, classy looking rifle, with a very nice right hand beech stock. It's long, about 44", and fairly heavy, but that's compared to the Talons I used to have. In truth, it's almost exactly the same length as a Gamo CFX. The FX is much lighter, almost shockingly so when you first pick it up, and about 4" shorter. It has a synthetic ambi stock with some rather nice grippy inserts right where they do the most good. The combination of weight, balance, and 8 shot repeater make this a great field rifle. I know the Cyclone is a more expensive rifle than the Whisper, I think it's because of the cocking system, although I can't quite see that alone adding almost $400 to the price. In .22, both rifles are rated at about 30 fpe, if my experience is any indication, they'll probably exceed that.
Just checked, the Whisper does NOT have adjustable power, both the 410 and the Cyclone do. BTW, if you want to come pick some apples and try the Cyclone and 400, let me know :-). Later.
Dave