This has happened to two of my Incredibles. It is clearly a hardware issue. The first one I got traded out for a new one after a year of use, and then when I just got my refurbed one it started doing the same thing again about a week after. This one does it a lot less frequently though. Glad to hear I'm not the only one with the problem.
Just for the hell of it, I was thinking my Seidio case might be causing it. Do you have a case on your phone?