What you said make sense, and it was the average of the whole file. I was the only one plugged into the pole, other than charging batteries, as far as I noticed. Both of the sets I've looked at so far are from different day, but its possible I used the same mics in the same place. I'll try to look at another one from a different day and see if it shows up in the same channel. Could it be the preamp? My ua5 has been ridden hard over the years and been around the block a few times.
<edit>
OK, I'm thinking more and more the problem is a tired preamp. the last set I recorded started out looking like this:
While the first looked more or less like this through the whole set:
Its unlikely I used the same mic in the same channel 3 days in a row and I doubt that one would "over heat", for lack of a better word. While I can imagine a preamp doing that.
In your opinion, should I even try to fix this? I'm listening on POS speakers so I only have a limited idea of what it really sounds like. Would it be better to just make it mono or copy the effected parts to the other channel when it doesn't happen often? Or, just trust my ears and only worry about it (as far as these sets go) when something sounds bad?