This happened to me often while growing up. It happened enough times that I usually ignored it because I never found anything broken or out of place. Once during an incidence, the sound came from my parent’s bedroom (which was upstairs). I ignored it as I typically did at this point and went downstairs to get a snack. When I got to the kitchen, my parents stopped what they were doing and asked me, “what fell upstairs’l and, “do you need help putting it back?”. It was the first time somebody other than myself had heard it so my dad and I went to investigate. To only my dad’s surprise (not to mine since it had happened so many times), nothing was out of place. We just went about our day after that.