It depends on the syndicator but it typically is an unencripted, repeating voice message with audio tones for level setting. Something like "This is the WestWoodOne Radio Network", "Right Channel 0db" BEEEEEEEEEEEEEP, "Left Channel 0db" BEEEEEEEEEEP, "Both channels 0db" BEEEEEEEEEEEP, and repeat... I should be able to quote it word for word as many hours as I have listened to it.
In the audio port menu, it is sometimes the only enabled program available.
If you have multiple audio ports, they can each be set to simultaneous receive a different program via the front panel menu or provider online setup site. Some receivers will not let you set more than one port to the SAME program
What kind of receive are you using? IE, XDS, Wegner I-Pump, Max, etc.