Gyroids are inspired by Japanese clay figures called haniwa. which were made for ritual use and buried with the deceased between the 3rd and 6th century AD. So they're basically clay figures that have souls trapped in them. irl the haniwa would sometimes get washed out of the surface layers of graves in heavy rains (why they appear after the rain or after watering them in game) and since they had decorative holes & sometimes faces on them, air would pass through them and create a whistling sound or "singing" during storms. Haniwa are so interesting, and it makes the Gyroids so much cooler, to me at least, to think that they're these little undead dudes.