My best guess its an unfunny "Easter Egg" that triggers after something like 5,000 hours of uptime. I think I remember some bug in Boeing or some other system that they need to actually be rebooted every 100 days.
The FAA does not agree with that. The FAA probably thinks that easter eggs in avionics software are a crime. And I agree with that position! Aviation, medical, military, and any other critical software should not contain easter eggs, and it should be an offense to knowingly include one. Stuff like this (even though it's probably not an easter egg) is a great example why. Just imagine the cost to patch this if it's widespread... and it has to be patched, because this one can literally kill people if you don't fix it (think spooked flight crews making rushed or generally poor decisions if you don't think this is potentially lethal).
According to the researcher who found it, "they didn’t think it was very funny.”
I love easter eggs myself—classic Apple software in particular had a lot of these, and I really miss finding them—but they're admittedly a risk. I remember one obscure Easter egg in Mac OS 7.6 that occasionally caused crashes at boot time after displaying a bizarre message about how "bluets and granola bars / make a chewy snack". Cute, but probably not something Apple wants to be getting customer support requests about.
As far as the topic at hand, I don't believe these weird noises are an Easter egg, either. I'd guess it's a recording patched in somehow by someone who works for the airline.
And that's what it boils down to, isn't it?
Personally I draw the line somewhere around "software that's controlling something". If software can directly screw up or cause damage in the Real World™, that's a good reason it shouldn't have easter eggs in it. If the trouble has to indirect through one or more meatbags who know better before becoming reified, well, the harm caused by any easter eggs is probably much less than the harm caused by reported bugs already closed WONTFIX with a laugh. (Note: PAX do not in fact know better, ever, as any airline employee can and will tell you.)
So boring! I look forward to my pacemaker giving me palpitations to the rhythm of "Never Gonna Give You Up".
Turns out his pacemaker was shocking him because it thought his elevated heart rate was a danger! They fixed the setting.
The B-52H bomb/nav computers had a really rudimentary golf game. Think Atari 2600 quality.
The B-2A had a breakout-like game at one time.
Both were accessed via some really esoteric key presses.