To get the From The Top of My Lungs achievement in State of Decay 2 do the following:
Screamers are the armless, shrieking zombies that attract other zombies. They're reliably found at Infestations, often more than one at a time too.
Track down four and kill them and this achievement will pop. Note that getting close to them will make them scream and temporarily disable your ability to fight. From a distance, they won't disrupt you in this way or possibly may not scream at all.