DAEs kid cover their ears when they fall asleep?!

Ok, so I have a son who recently turned 3. Our bedtime routine has been fairly consistent; with him, my husband and I all cuddling in his bead and having 20 min of tv time and then the tv goes off whether or not he's sleeping yet.

Some nights there a little bit of whining and others he just rolls over and goes to sleep. These last few weeks I have noticed if I turn the tv off he closes his eyes really tight and covers his ears, as if waiting for a loud sound. I've taken his hands off his ears and told him that, "it's ok, there's no reason to cover your ears," and he responds with "Monsters mommy" 😳 then falls asleep like its the most normal thing in the world to say!! Then I'm the one who's left wide eyed and awake!

Does anyone else's kid do this or something similar? Mind you he just turned 3, so just asking him why he does that isn't going to get me very far