GeorgeF ...

^ ... I had 7 scanners setup, each scanner setup to scan
^ a 25 MHz segment of the 225-400 MilAir band.
^ Everything was going fine up until 1048 hrs EDT.
^ 5 of the 7 scanners stopped with what sounded like a
^ data signal.

^ Here are the freqs which had the very same transmission:
^ 225.0000
^ 275.0000
^ 300.0000
^ 325.0000
^ 375.0000

^ The transmission lasted for about 3 minutes and quit.

Did the other two scanners cover 250.0 and 350.0?

Coincidentally, while I was reading your message (abt 1825Z) I heard a loud
klaxon-like sound coming from one of my scanners. By time I got over to the
scanner the sound had stopped but there was still a carrier holding one of my
39MHz frequencies open. The klaxon, which did sound like a data signal, only
sounded three times for a total duration of about five seconds. It's probably
not related to what you heard.

Frank