These are Skywalker Sound sound effects. They were created by Ben Burtt, and they debuted in Star Wars: Episode V - The Empire Strikes Back (1980) for usage on the AT-AT walkers. It was used again in a pitched up variant for the AT-ST walkers seen in Star Wars: Episode VI - Return of the Jedi (1983). The 2nd take should not be confused with the similar sounding SKYWALKER, METAL - SHORT HEAVY RATTLING, RESONANT. Links: https://soundeffects.fandom.com/wiki/SKYWALKER,_METAL_-_AT-ST_STOMP#Audio_Samples