I don't hear any footsteps at all.

Gunshots, dialogue, and explosions are heard loudly, but nothing is heard except the sound of footsteps.
The enemy approaches without a sound. Always suddenly, the enemy comes up behind you and shoots at you.
I can't turn the volume up any higher because the other sounds are too loud. How can I hear the footsteps?

I need to be able to visually see the enemy's footsteps if possible.