This is a Skywalker Sound effect that was recorded by either Randy Thom or Tim Nielsen, and it is not available on the Lucasfilm Sound Effects Library. It's most notable usage was being used as the whistle sound on the locomotive in the 2004 motion-capture animated Christmas film, The Polar Express. It is also where the sound effect debuted. The whistle that is heard in this sound effect is a Lima 5 chime steam whistle that was recorded from Hollywood famous steam locomotive, Sierra Railway #3. (An 1891 Roger's built 4-6-0 "Ten-wheeler" steam locomotive.) However, it is possible that it might have not been recorded on #3, due to the fact that she had been out of service at the time since 1996. And any videos and recordings of her before 1996 do not sound close to the whistle used in the film. There is a possibility it could've have been put on #28 (A 2-8-0 "Consolidation" that also works on the same railroad.), but this is up to speculational. Links: https://soundeffects.fandom.com/wiki/SKYWALKER,_TRAIN_-_POLAR_EXPRESS_WHISTLE#Audio_Samples