It could be the hard drive failing. In that case the DVR would need to be exchanged and you would lose the recordings on the DVR. It might get worse and will eventually stop.
It can also be signal issues coming into the TV outlet for that DVR. A tech visit would be in order to check, confirm and correct the signal issues.
You can try to swap the DVR first and if that doesn't fix it, then Comcast would need to send out a tech. If you take the DVR to the local office, take the remote with.
