Reminds me of when a security researcher discovered that, in addition to some serious security flaws, certain Siemens PLCs had monkeys hidden in their firmware: https://arstechnica.com/information-technology/2011/08/serio...
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.