Morning from the UK!

Apologies if this has been answered (can't seem to find a definitive answer though..) - when moving zombies and all survivors are inside and no line of sight to them, do the zombies walk towards the nearest noise even though there is no open door. If so, do they just wait by that door or if there is an open vault which is further away to get to the survivors do they head towards that?

Hope you can help