Not sure if this applies to you, but if the meter bangs of its limits a lot (clips) it will mess it up. It can also happen if it gets left on and picks up sounds that cause it to clip too.PROBLEM SOLVED!
From the last experiments I suspected the SPL meter and sure enough; replaced it and all works reliably. I want to thank all the many writers that helped narrow this down. An intermittent electrical problem is the worst and most frustrating.
THANKS ALL. With a fixed tool I can now fixate on the acoustics!http://www.hometheatershack.com/forums/images/smilies/t.gif