RE: sneaking
Was looting around the NW airfield with a buddy, at first we went in all sneaky, proning around the zombie sentries etc.
After my buddy got spotted through a wall by a zombie on the other side while looting, knocked down and the zombie was invincible to my shots due to lag, I raged and went full retard - took out the AK and ran down the landing strip, from North to South. Trained about 15 zombies on me while going past the control tower, but they lost the LOS as soon as I went into the next hangar. They didn't hear me shooting their 3 buddies inside either.
So, in the end, running around and pre-emptively shooting zombies seems to be the way to go these days - they are pretty deaf, but have eagle eye sight.