Here's the link to the new firmware update which should fix the issue:

Canon EOS 7D Firmware Update

Hey Trav,

Did it fix the issue for you? I'm going to upload it to my cam in a bit and test if it gets rid of the split second overexposure in my clips when I first hit record, which happens randomly.

Don't know yet. I just updated the cameras last night. I have a shoot in 30 minutes so we'll see. The issue is intermittent, so it's going to be hard to know if it got fixed or not right away.

Bill is correct.

Bill is not correct, and I've already explained why. It was a good guess but it is incorrect.

I've had this exposure shifting happen in other situations where the camera was locked down static. I had a shot of some wedding programs with nothing but blue sky in the background and I shot a timelapse (just ran video). For no reason, after a minute or two, the sky lightened. I had another timelapse of a sunset and as the sun had nearly set the sky suddenly lightens. I also had an indoor static shot of a groom buttoning his jacket and the exposure of the scene lightened just slightly for no reason.

The fact that there is a firmware update addressing the problem (and hopefully fixing it) shows that this is not simply an issue of a change in light entering the camera.

Still no manual audio. WTF Canon!