Bullet crack, whether it's 17 hmr or 22LR supersonic or a 223 is basically the same.
With subs and a bolt action and a longer steel suppressor, a 22 LR is the same as an airgun. Maybe quieter. I'm sure if you made the suppressor big enough you could get it as quiet as a whisper, but most of them now are quiet enough to shoot in a house, or shoot varmints from your deck without alerting the neighbors.
There is actually a big difference between how well 22LR suppressors work; the older designs are much louder and speaking generally the aluminum ones are louder. This is really pronounced on pistols and less so on rifles.
My integral 10/22 with subs is so quiet that, as mentioned before, you just hear the action running.
The sound of the bullet hitting the target is also pretty loud.
