reply to UnexplodeCow
Re: Inconsistent, unreliable internet service (Help needed) There is no specific time when it's crummy. It happens at any given time, and I've tested late at night (2-4 in the morning), 8 AM, 12 Noon, 4PM, 7, 8, and 10PM, between the weekend and this week. It's one definitely bad channel, and another isn't looking too healthy, either.
The only splitter installed is an RFI trap on the outside of the house, at the box (which has dirt and spider nests in it). The trap in question looks a bit oxidized.
Basically it comes off the pole to the RFI trap, to inside the house, hits a single straight-through connector (not a splitter, just a butt connector), and on to the modem. We don't have cable TV here (pointless because I stream, and rely on internet for that), so there's no need for a splitter. I might still have a 10dB tap sitting around to cut down signal.
I suppose I could try putting the modem outside briefly (run an extension cord and long ethernet line), and see if that will make any difference in determining where the noise is coming from, but after seeing the cable box outside (at house, not at the pole) I'm inclined to think it's more outside the house than in.