Quiet enough that people don't call their hits.

Seriously though, it's awesome, and pretty much the only redeeming aspect of a low-grade bolt gun. I haven't even done much to it, and at 50 ft, the only sound you're gonna hear is the BB. (Usually whizzing past your head, 'cause I don't have a good hop yet, but still...)

 

Same here KingsWit. I've never put a meter beside it, but at more than 50 ft away, it can't be heard. My effective range is still pretty good, but everything just works together and you hear nothing. In fact, it's almost disappointing.

 

My Well MB01 can't be heard from 40-50ft away

 

With the suppressor, my Tanaka only makes the trigger mech 'click'.
...
It's a pretty big suppressor.

 

Quiet enough that the BB through the air is louder.
The sound signature is more like something firing a slingshot (note: i know nothing about slingshots).

 

Quiet enough that the BB through the air is louder.

That is similar to mine. That is annoying because if you miss, the target can figure out where you are from the sound of the bb whizzing past them. Then it does not matter if your gun is quiet because your bb sound gives you away.
I guess the moral of this story is do not miss your target first shot.