Used to shoot CB's all the time in our Collage dorm room, never any complaints from the neighboring rooms.
Could be one of the reasons collages are so against any guns on campus.
One of my buddies took an old ranger .22 semi auto and suppressed it. I don't remember what kind of can it was but it was quiet. You could push the charging knob in and lock the bolt turning it into a straight pull single shot. As I remember it was very accurate but with that long barrel and big can on the end it was way long. He was talking about cutting the barrel and magazine tube back some but I don't know if he ever did.