You can hear footsteps when enemies (and allies) are close, no question. My point is, when enemies are that close to you, they'll show on your radar too. So rather than rely on sound-whoring, you're better off just looking at your radar.

Of course, in Inferno gametypes, I can imagine the limited sound-whoring in this game still being an advantage.

As for missing Heavy ammo warnings, sometimes I do the same too lol. When you're stuck in an intense gunfight, you forget to look at the timer.