Silencers are very badly named honestly. A "silenced" gun is still very loud, it's just moderately quieter than an unsilenced one. People watch movies and TV shows and play videogames that make it seem like a silenced gun barely makes any noise at all and think that's reality. That is very much not reality, it just makes for a more entertaining story.
I could be full of it.... but I think that's because those rounds are intended to travel below the sonic boom threshold resulting in less noise when using a suppressor.
A unsilenced 9mm out of a handgun is normally around 160db (assuming common ammunition and a common type of handgun). A reduction to 125db with a silencer seems about right.
Edit: Here’s a silencer talk link that goes very in detail. For their chart, 125 db is actually very close to the low end, with many suppressed shots being louder.
FWIW I believe those measurements are right at the silencer while the thunder measurement I find is “within a few hundred feet”. There can be quite a significant drop in perceived noise from silenced guns with a moderate amount of distance making them sound like a distinct but not overly loud“thwack”.