I could always hear a builder tapping away, must have been across the way as sound travels along a solid surface. Regular even taps, like putting nails in.
It was always when I was upstairs in my sewing room. I saw the culprit today, young jackdaw, not his partner, he was tapping into an acorn with his beak, holding it between his feet at the top of a solid fence post.
He stands on my ridge tiles and does the same tapping, my garden is strewn with acorns with holes, never used to get any and there are no oak trees nearby. This jackdaw has befriended me and my garden. It has never happened in the five years I have been here. He is very clever, chose to tap the acorn against something hard
Yours oreo does sound like mice, if it was higher up it could be rat, squirrel or bat. If there is a cavity wall it could well be a rat, they create tunnels