I get either 17 or 23v. But that changes depending on which channel is being watched. That would seem to make these related to the selection of LNB polarization.

I'm guessing that this shouldn't be a cause of the pixelation, unless maybe the LNB is being switched when it shouldn't, causing dropouts.

Further web searching yielded numerous threads about power supply problems causing pixelation or crashing. There are also reports of marginal supplies causing problems, on one tuner, when an additional output like composite out or svideo is connected.