I thought that was "normal behavior" for MA. I am sure that I have a Vista Ultimate 32 system with MA2.6 that continues to play the "bubble sound" after the monitor is turned off (by the automatic power settings) - at least as long as the computer doesn't go into "standby" or "hibernate". [Perhaps your settings are different, though].
I'll have to test that on MA3 when I get a chance. Or, Jim can tell us what the sound is supposed to do under various conditions.

I can confirm that on a WXP Pro system with MA3 installed, and the screensaver set to activate at 1 minute, and the monitor to turn off after 2 minutes (and no other power-saving settings), after an hour the bubbles are still merrily burbling in my speakers.
That seems, to me, like normal and expected behavior.
But perhaps Xylem was reporting a different set of conditions?