Sounds in Unreal Tournament aren`t only existing to make the game more realistic and more fun to play, they also help a lot to figure out where your opponent is and what he is doing there.
The most obvious sound to achieve this is the footstep-sound, but it isn`t the best one. Even with headphones it is difficult to determine the exact direction, where the sound is coming from, same thing for distance and height level.
Much more distinctive are pickup sounds of weapons, ammo, health and armors or elevator/teleport sounds, or water sounds, because these are always typical for only few locations.
In Codex for example, if you are at the armor and hear someone take an ammopack and a weapon you can be pretty sure, that he is at RL and will drop down to the vials/armor shortly after that. And if you are quick enough he will drop into your combo.
"someone just picked up a weapon and ammo nearby"
"it sure was the rl and rockets, so he will drop down soon, I`ll better make a combo"
Or you could wait at the top of an elevator and shoot as soon as you hear the sound.
A good trick is not to take all the health vials at one place, so that you hear if he is going there because he will most probably instinctivly collect that last vial.
I could list dozens of examples now, but all you need to do is to stop hearing the sounds, start listening to the sounds...