I was just mining a new tunnel so i could get a lot of stone and i heard that growling noise a zombie makes. My whole self made tunnel was fully lit so it must have been an adjacent tunnel. I stopped mining then because it sounded like 5 or 6 zombies and i had no sword/armour. I was like: "holyedgfkojhwsegfjherdhedi"
EDIT: OH MY GOD THAT ADJACENT TUNNEL IS UNDERNEATH MY HOUSE.