Do they sound the same

The PCP is generally lauder unless it is shrouded. However, a non tuned springer can be twangy and laud too so it all depends on the model. For example, I had a cheap Crosman springer that was very laud. So give us the rifles you are curious about and we could give you more specificity. In general though, PCPs are lauder. If you have something like a Talonp without a moderator it sounds like a 22lr on full power. Most PCPs are lauder than a springer.
 
Springer is less laud, usually. My tuned hw95 is very quiet compared to most PCP, about 1/5 the noise and no twang. If you shoot a single stroke pneumatic piston in the magnum class, the noise can match a PCP sometimes. The noise also depends on the caliber. 



Think of it this way: in one gun you have an a valve being opened and all the air being released for that shot in an instant. On another rifle you have the piston or spring moving along and pushing that air in a not so efficient process that is not instant. That air takes longer to get out, and there is more noise at a lower decibel over a greater period of time, and the PCP has a higher dB for a shorter amount of time (usually). 


Hope that is more straight forward.
 
PCP depends on what brand and model. If it's a STEYR it sounds like a 22 Rimfire. Others range from a balloon pop to a car backfire to a CB 22 or a nail gun. Compared to a Springer that sounds like a staple gun or this...

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YO's post is TMI for me BUTT.......

Why fart and waste it when you can burp and taste it?

Did you ever walk through a crowd and "crop dust" them?

Seriously though. Not all untuned springers twang. Mostly just Weihrauchs. LOL! They make up for it with a superior trigger I guess. 👍

I can make a spring guide easy enough. Can't think of anything that machines easier than Delrin. Not so easy for me to make a quality trigger mechanism. 

I think pneumatic blast is louder than a springer that produces similar fpe