Making noise is not a really big issue, Unless you are in a house smashing everything you can usually get away with getting in and getting out without being caught.
The problem with sneaking is, monsters have a 360 degree vision, so unless you are obscured from their site, they can spot you anyway.
Personally I would prefer it if zombies got a big decrease in their viewing range, and were much more sensitive to sound/scent.
That way we could spice up the game quite a bit with “sneaking” and perhaps some kind of scent blocking mechanic (like the bionic, but less effective and cheaper).
It would also make guns quite a bit more balanced, rather than a town clearing machine.