[joezydeco]

The new sound is even worse (and seemingly longer), and I imagine it's signal (which sounds more like fax machine squelches than an alert noise)

This is the SAME (Specific Area Message Encoding) header, designed to deliver more detail to receiving devices about where the event is, the type, and how severe it will be.

https://en.wikipedia.org/wiki/Specific_Area_Message_Encoding

This is how you can buy weather radios that only deliver emergency weather messages for your county or town as opposed to the entire listening area of the station.