I do have a 68Kohm resistor between the jack tip and pin 2 of the 12ax7.
Tonight I put together an “audio probe” as per the instructions on the billmaudio site (thanks Robin for the suggestion!):
I wasn’t able to locate where in the signal path the noise begins, because I have to have the amp turned up too loud for nighttime use in order to consistently generate the static noise. I’m hoping that I’ll be able to locate the problem component with this probe.
Thanks for the continued suggestions,