Finally got around to looking at this today. Of course Mr. Scope confirmed Kevin's diagnosis (and cure); it was definitely oscillating. 200 ohms in series with the pot wiper -> amp took care of it.
Funny, it didn't oscillate when I built it and worked on checking dc offset (with board input shorted). Must be the additional inductance/capacitance of the input and pot wiring. I would guess that had I board mounted the pot (this is one of Justin's V2 boards), it would not have done this.
Thanks for the quick help Kevin!