Another debugging trick is to get a test lead with alligator clips on both ends, ground the grid of the first, and then the second 12ax7 tube, and listen for the noise to go away, that will isolate the problem to a section of the circuit that way. Unplug, let the voltage drain from the caps, check that with your voltmeter, install jumper, remove hands, then power up and listen. Don't do this on the 12au7 tube, its grids are direct coupled and not at ground voltage.