Odd behavior of OD Drive pot - need help "solved"?

[mlp-mx6]

OK, I was able to play it today (out of town yesterday) and the tone/drive is fine. I'm happy. Still a bit perplexed, but happy.

Fischerman, the long runs I was referring to are from the plate output of OD1 to the grid of OD2.

I do not think these were the location of the coupling since the source of the oscillation was the OD1 triode, and because the cause was to pull the OD1 grid closer to ground (turn down the trimmer). So long as it works and sounds good, I'm ok with it.