The problem isn't about the difficulty but the common sense, now zombies will hear you or see throught walls while you are crouching on the second floor at 1 bar noise, they also will usually hear you most of the time when you will try to get stealth kills, once one is alerted most of them will come and even more will aggro from the surrounding.
Not that I don't like the feature but the real problem is about the zombies being as broken as they are, they glitch and can go throuht walls, doors, will stuck you inside the walls, will teleport on the rooftop, will hit you from behind, will run like headless chicken before comming back to hit you from their own back, they are also broken on the pathfinding side, going from one side of the door to the other one again and again, jumping the same fence many times in a row, will aggro you even if you are laying in the bushes or grass while they were originally aggroed by someone else, or some shots from far away. None of this makes sense and ruin as much the gameplay as the coherence and the immersion.
What we need is a real organic increase in the difficulty because of their behavior, not something artificial to balance a bad behavior/coding. To be honest the ones we had before this patch were good enought and did not really needed any change waiting for a real rework, now most of the encounters feels weird and unnatural.