Hey Fryy,
Thanks for posting that very interesting clip...just wondering, did this clip come from the PGUM or the RPLL feed? In addition to the US and Chinese military comms there's also civilian aircraft that can be heard. DAL166 can be heard plus a number of other aircraft. There was even an aircraft requesting FL430...it sounds like this is a radio scanning other frequencies in addition to guard.
My guess is that he noises (sirens?) that can be heard might be alert/warning tones of some kind. It seems like they only occurred when the "Chinese Navy" was transmitting...just a guess...