This could be caused by a weak signal, which can affect only certain channels. Check the connections to the cable box, especially the incoming coax, and eliminate any unnecessary splitters.
To check signal strength with a Motorola box, tune to the offending channel, turn off the box with the remote, then within two seconds hit "OK/Select." This will bring up the diagnostics screen. Select "Inband Status" (probably page d04) and look for "SNR" for the tuner(s). This value should be in the mid to upper 30s. You may be able to improve the signal strength by adding a signal amplifier to the incoming cable line.
It also may be a weak signal caused by problems outside your house, in which case a call to 1-800-COMCAST to have them send out a tech to check on it may be of benefit.
I am having the same trouble. TNT, TBS, USA, E! apparently all the channels that I watch all the time are appearing to "lose a signal" (which does not make sense because I do not have a dish) or completly freezing up. I went through the online info as to whether I will need to change boxes and it tells met that since I can see the "on demand" menu on channel 1 (after a long delay) that I don't need to change out boxes.... does not make sense.
War Eagle is correct - weak signal. It could be from bad connections, especially if you are using homemade cables with twist-on connectors. It could also very well be a problem from the street to your point of entry - if you try my next suggestions and they still don't help, then Comcast needs to send out a tech and have them check the line to your POE.
I had the same problem; I ditched my 'homemade' cables and replaced them with new pre-made quad shielded outdoor cables, rerouted everything so that my STB and modem were off the first splitter and my DTA's off the second, and added a signal amp in front of the first splitter. Now I never get a loss of signal and my internet connection seems faster.
I agree -- seems like Comcast should take care of this -- I don't want to call them on the chance that it might be outside, then discover it's inside and they slap a big fee on my bill! I didn't do anything to create the problem -- it just happened all of a sudden after working just fine for months! So I would assume it's either their box or their wiring and I shouldn't be responsible for repairing either of them. As I mentioned, my box hums loudly and I'd like to have a box that doesn't!
Any cables that are connected to the POE or to my TV were installed by comcast - not homemade. As for War Eagle's suggestion, he clearly states "on a Motorola box" and mine is Scientific Atlanta so I assumed it wouldn't be the same. I don't have any unnecessary splitters - just one TV and a modem. I don't know what a signal amplifier is, but don't think I should have to add anything to make equipment that I don't own work better! If we must rent their equipment without choice, then comcast should provide whatever it takes to make it work the way it should with the best possible HD viewing capacity - be it better cables, better STB's or signal amplifiers.
To jaslines - STB means set top box; POE is point of entry; don't know what a DTA is but just guessing I'd say it's a digital transmission device.