17hmr with a suppressor is very quiet. Not quite as quiet as a subsonic .22lr, but very quiet. I can shoot consistent 1" groups at 100 yds with mine, where my 22lr shoots 2"+ groups. Even larger groups when shooting subs. With my 17hmr I've shot rockchucks off a pile of wood stacked on the edge of a garage, without having to worry about the bullet passing through and going through the wall of the garage. I wouldn't take that shot with a .22lr. The high speed light weight 17gr .17 bullet disintegrates upon impact and distributes all its energy. That's one of the reasons I like it for around structures.
Yes PCP cost as much as a firearm, but if you want ultimate quiet pest removal, it's hard to beat. It's been my experience that most firearms aren't optimized for subsonic ammo, (throat depth, case volume, barrel twist rate, bullet shape, etc). Even if they are, many powders don't burn clean at subsonic loads and result in a fouled up barrel (especially when using a suppressor) which then degrades accuracy. PCP rifles, set up right, are optimized to shoot subsonic accurately, and they can do it all day long and never foul.
Competition grade PCP's can shoot 1/2" groups at 50 yds. Good enough for headshots on squirrels. I usually don't shoot that far with mine. But mine will do 1/4" or 1/8" groups at 20 yds.