You guys are reading way too much in this. It's obvious they are in the panic room. It is sound proof but not completely. So cclinking sound they hear is muffled from their side probably loud from the other side as those guys are really tearing up the place. They are scrunched together because they are huddled against the wall on the other side because what if the room is found? you don't want to be standing in the middle of the room if they break in
Really already explained the soundproof thing. They could hear a crash and clinks can get loud (could also be an odd translation). Honestly the room itself might not even be soundproof. That could have just been something Asami said to intimidate Akihito. Ever thought of that?
If the room were soundproof, Asami wouldn't be telling Akihito to stay quiet.
http://www.mangago.zone/read-manga/you_re_my_loveprize_in_viewfinder/mh/v08/c051/18/ in this panel there is this sound "clink" mentioned in a bottom like opening a door ou clinking two glaces it's a very soft sound, if asami & aki can hear this sound they are definitly not in panic room! i'm sure NOW. crash sound ok, assasins speaking ok the materials of this panic room can cheap but a clinking sound NO. sensei never failled to suprise me she is very smart and can't make sush mistake. (๑•ㅂ•)و✧