Myself and my friend have been playing this up until day 20, and we've been getting at least 3 screamer hordes per day for the past 6-10 days, and these aren't small hordes either, being like 15-30 zombies strong. I believe our difficulty is one above normal, and it's becoming a huge struggle and obstacle. I like the mod, and I don't remember it being this hard when I last played it. Maybe I'm wrong though.