It will depend entirely on if they plan on trying to get into the locked doors. Just on foot, they will be able to move through the hallways in a completely horizontal manner. They can walk for as long as they'd like, but the sound does not seem to get louder/softer where you move. There is some change in the distance of the sound between noises, but it seems to be done on its own.

You can certainly tell the sound is below you. But there isn't much else.