The sound of the TARDIS arriving is an unmistakable — and distinctive — sign that the Doctor is near. But, while the sound may be alien, it turns out that its origins are decidedly earthbound.
After looking at the series of keys that have opened up the famous blue box throughout the years, commenter simon-on-the-river3 pointed out that there was also another key that had a claim to be the first to belong to the TARDIS, though in a completely different way.
The wheezing of the TARDIS was actually generated when Brian Hodgson, then the studio manager at theRadiophonic Workshop, dragged one of his house-keys along the strings of a broken piano. It's a story that Hodgson also confirms, and goes into detail on, in an interview with Radio Times:
"I remember a phrase about the 'rending of the fabric of time and space'. So I wanted a sort of tearing sound. What we definitely didn't want was a sound like an ordinary space rocket. When I first sketched it out there wasn't a rising note, but Desmond insisted we needed one or else it wasn't saying "spaceship" enough. So we put that in." The sound was generated using a broken-down piano frame. "It was standing up in the corner of the workshop with its strings exposed and I scraped a front-door key down the bass string. We recorded that and added loads of feedback."