I'm adding a config file to every save so people can experiment with spawning behavior. This also adds the "population starts lower and gets higher over time" thing. Or you could have the population start higher and get lower over time.
Spoiler # Same as the sandbox "Zombie Count" setting. # 4.0 = Insane, 2.0 = High, 1.0 = Normal, 0.35 = Low, 0.0 = None. # Minimum=0.0 Maximum=4.0 Default=1.0 PopulationMultiplier=4.0
# Adjusts the desired population at the start of the game. # Minimum=0.0 Maximum=4.0 Default=0.8 PopulationStartMultiplier=0.2
# Adjusts the desired population on the peak day. # Minimum=0.0 Maximum=4.0 Default=1.2 PopulationPeakMultiplier=1.0
# The day when the population reaches it's peak. # Minimum=1 Maximum=365 Default=28 PopulationPeakDay=28
# The number of hours that must pass before zombies may respawn in a cell. # If zero, spawning is disabled. # Minimum=0.0 Maximum=8760.0 Default=1.0 RespawnHours=24.0
# The number of hours that a chunk must be unseen before zombies may respawn in it. # Minimum=0.0 Maximum=8760.0 Default=1.0 RespawnUnseenHours=1.0
# The fraction of a cell's desired population that may respawn every RespawnHours. # Minimum=0.0 Maximum=1.0 Default=0.1 RespawnMultiplier=0.1
# The number of hours that must pass before zombies migrate to empty parts of the same cell. # Minimum=0.0 Maximum=8760.0 Default=1.0 RedistributeHours=12.0
# The distance a virtual zombie will try to walk towards the last sound it heard. # Minimum=10 Maximum=1000 Default=100 FollowSoundDistance=100
So, I've digged around in PZ files within the game, and found some pretty cool and unused sound files there. I won't be teasing you too long and will go straight to the deal.
When your character gets the fever/bitten, the "Stress" moodle pops up, eventually coming to the extreme level where it says "On Edge". What I thought would be quite cool to be played on background when the moodle is on (keeping both you and character "on edge", heh) :
Have it play randomly in 1-3 minutes.
2: ProjectZomboid\media\music\ambient1 and ambient2
Have those play a bit more often than the first one.
Additionally, add non-existing door and window thumps so player constantly stays paranoid and thinks that there's a zombie knocking on a door.