It may be a wrong and long-stretch of an idea, but what if this is an audio being played into that headphones jack at a seat?
Directly, this should not be possible (input vs output on the amp), but in case the PA mic signal is routed to common amp after keying and preamp, this technically may be possible.
Now, if the "keying" includes some specific signal to allow the routing to PA, the question is if the "keying" signal can be sent from the seat's console. Then just play back the annoying track into the headphones jack.
Linked article appears to state the PA system is physically isolated — which I would assume means only known components of the PA system interact with each other:
>> Professional reverse engineer/hardware hacker/security analyst Andrew Tierney (aka Cybergibbons) dug up the Airbus 321 documents in this thread, and is stumped too.
I vaguely remember that PA messages are heard in headphones, so the PA signal is being patched through at some point.
It's not clear how the "seats" bus is isolated. I assume it's a bus, so that seats are addressable. The seats should at least be able to send the "need attendant" signal.
I hope a qualified technical analysis already pointed a few possible vectors for this. The question is in remediation and, well, identification of the perp(s).
Either way, at this moment the story seems to act more as an attracting magnet than repelling for the airline. Back during summer, it certainly was another level of annoying and disturbing.
Directly, this should not be possible (input vs output on the amp), but in case the PA mic signal is routed to common amp after keying and preamp, this technically may be possible.
Now, if the "keying" includes some specific signal to allow the routing to PA, the question is if the "keying" signal can be sent from the seat's console. Then just play back the annoying track into the headphones jack.