CableCARDs causes Tivo HD to hang+crash?

I have a new Tivo HD (the $300 one), and last night Charter came out and installed two Motorola CableCARDS. It ran fine for about an hour (both cards receiving/decoding fine), and then it locked up making a static-filled buzzing noise. I ended up pulling the plug to restart it, and it went into a continuous reboot cycle, where it would spend a few minutes on the first boot screen, switch to the almost-there screen for a few more minutes screen, buzz for a few seconds, and then reboot again. It kept doing this.

I pulled both cablecards, and it booted. I reinstalled both cards, and an hour or so later it locked up again with the buzzing noise, and went back into the continuous reboot cycle after a power cycle.

Then I tried installing only the cablecard in slot one, and it ran fine all night.

My question is: what is the cause of the problem? Do I have a bad cablecard in slot 2? Is it a software problem and I need to wait for another update? Or does the entire box need to be replaced?

I called tivo tech support, and the guy I talked to said he thought it was a software problem (and verified that I was running the latest release), but this guy didn't impress me as being very knowledgeable.

Has other people experienced this? What should I do next?

Thanks!!!