reply to UnexplodeCow
Re: Inconsistent, unreliable internet service UPDATED An update, and a close for this issue.
I did manage to request a tech to come out and take a look at things, as I was getting a few million errors a day on one channel, each time the snow melted here. The tech found the reason, which the picture is of. Apparently a tree was rubbing against the line, and had rubbed through the outer insulation, ground braid, inner insulation, and partially through the center wire.
I have to admit that I'm pretty happy my modem was able to work with that at all. SNR is up to around 38-39 on all channels, no errors, with new cable from the pole to the house. I can't fault the tech for quickly finding the trouble spot and fixing it quickly. Speeds are back up to a steady 30.8M down and 3.3 up, so a small increase over what I already had.