My T does not, but at most, I've only ever met his next client passing on the stairs. Noone ever waits in the 2 chairs in the hallway, my and the other T's in the flat always have their patients wait in their room.

My current one does not, but I've never really heard much in the hallway and definitely nothing from the waiting room--the way it's laid out, it's fairly distanced from the actual offices. They did use white noise machines outside the doors at the first location of ex-T and ex-MC's office (don't think they had at the second, I forget). I think they helped, as I didn't hear anything from the waiting room (well, aside from a client, I think a child, screaming, but a white noise machine won't help with that!)

I do think it could help to have it inside the room, too. When I've done Zoom sessions at my house, I use both a fan outside the door and a white noise machine inside the room. If nothing else, I think the white noise would help to sort of blur/muffle the sound, so it would be harder for someone outside to hear what you or your T were saying.