Well, now it hasn't done it in a few days. I did have the Automatic Volume Control (AVC) up over halfway on the sensitivity scale. I haven't turned it off yet, but then I like not having to turn the volume up every time I get on the freeway and down again upon exiting. I drive I-90 to and from work. I guess I have to decide which annoys me more.
Thanks for all the help, everyone. The pattern under which it does occur is consistent with what you describe, salsbr; sudden changes in speed through braking for example.