An 'auditory hallucination' mod - that is, a mod that makes the player occasionally hear enemies that don't even exist. Imagine you're exploring a level, and you hear a Cyborg Midwife marching in a nearby area, or vocalize the line 'I'll tear out your spine' behind you - only to discover there's nothing there. 💀 I have no idea if this would be possible, but this would really increase the paranoia of the player. It could also be an extension of the lore of 'residual psychic emanations' that makes the player see ghosts, only auditory rather than visual. What do you think?

Originally submitted this idea as Insect124, but I've done this with the cargo bay now:

https://www.systemshock.org/index.php?topic=12304.0