Strange noise at Cardiff Central

[tfw756rider]

In this video at Cardiff Central by Jack and Ed, shot in July 2026, a strange noise can be heard from about 4 minutes to the end of the 16m 47s video. They were wondering what it was, and I'm wondering what it was too. Does anyone in here know what was making it?

 

[Martyr]

You don't mean the seagulls that can be heard? Get lots of those at Cardiff Central.

 

[tfw756rider]

Perhaps I should've been clearer (I don't consider seagull cries to be a strange noise).

It's more of a continuous noise during the latter 12 minutes of the video, as if the whole area was fan-cooled or something (the noise doesn't come and go with the trains).