I was shearing some sheep as one does when the sun set and I heard a sound zombie growl. I looked around me and walked a few blocks in a circle and didn’t see any zombies. only one skeleton (who made its usual noises). Now I can’t use my bed because of that game rule. So the game also must think there is a zombie nearby.
If you hear a zombie growl, there is definitely a zombie nearby, whether it's in a cave or somewhere you haven't checked yet. In a test world, you can use the following command to teleport all zombies within the bed radius to you, to confirm their presence.