Items that are bounced off the map by say meteors or using automatic dispenser remain on the map. Just being one tile away, and creating continuous hitting sounds. They are reachable by duplicants or sweepers.
It persists on saving/loading.
I was trying to get rid of extra abyssalite and other crap.
Use automatic dispenser turned to the tile that is not visible on the map. Or hit an object on a bunker door with a meteor that bounces it out.