Ever since a couple of months ago, my TiVo HD has had trouble getting reception with a few channels in our lineup. Most of our channels come in just fine, but a handful of channels scattered through the lineup (most in the 40-60 range, but some others that are higher) get only a grey screen when I tune to them.

I called the TiVo cablecard hotline a couple of times but the only thing they've ever told me is that my signal is too strong (signal strength shows at 100 on the DVR diagnostics screen). I bought some coax attenuators online and put them inline to drop the signal strength, but this did not affect anything.

I have tried rebooting the TiVo many times, repeating guided setup, etc. The odd thing is that the SD channels that I'm missing (47, 52) come in just fine if I remove the cablecard, but I lose them again when I reinsert the cablecard.

The cablecard is activated correctly, and I am receiving our premium channels. Comcast sent a tech out and he tried 3 or 4 different cablecards, but to no effect.

Any ideas or other things I could try?