I for one welcome these new ambient sounds. I'm with @Geez here. I can't reproduce player footstep sounds at all. All I hear is dear Mother Earth's breath, exhaled amidst her rather prickley body.. hair..

Have noticed this as well. Too many infected in one area (outside of house/building - aggro'd on player) will even go as far as cutting off player made sounds. Available audio "channels" flooded? As in, some limit for however many sounds can be produced in one given area is reached so no additional sounds can be produced?