[X4U] Odd "bing" sound, every 10 minutes~

[keith_w]

MDD G4 tower, OS 10.4.8, using SeaMonkey 1.0.6 suite.

In the past day or so I've noticed an 'announcement' that appears as two 
beeps, 3 seconds apart, with the first beep accompanied by a 1/2 second 
flash of some small window, that has text in it.
Too fast to read, so I have no idea what's in the window.

This announcement repeats reliably every 10 minutes.

Who has an idea what this might be?

keith whaley