Many of Sidewinder style systems use a "tone" to indicate their lock-on state. The tone is low when the system is turned on but not "locked on". It quickly rises into a high pitched tone when it's pointed at something hot. The user is expected to first "cage" the missile, straightening out the sensor, then point it at the target, then "uncage" it and swing around to ensure the change in pitch matches your expectation. Then finally it is to be fired.

We in the public don't have a complete list of missiles from various nations and their tones, but it's well known that American Sidewinder systems use an iconic growling dog[1] tone. Stinger is more sine like[2], and many others appear to be sine like too, and newer systems like 9X and later are clearly just digital and software based even by public descriptions of it.

What I'm suspecting is that, the early gen Sidewinder growl might have been just the raw sensor output piped into the headset, because the operating principle of those seeker units somewhat corresponds to the sounds, down to the high boresight angle warning tone which isn't hard to imagine a kid playing with a benchtop example and accidentally implementing it by damaging some cable.

1: https://www.youtube.com/watch?v=OttbRzLr3VI

2: https://www.youtube.com/watch?v=Y_dQMlwAAYM

I think he's actually referencing this (the sidewinder lockon sound): https://www.youtube.com/watch?v=z2rDGC2TPGE