Just to close the loop here, I ended up retubing since the tubes were original near 18 year old tubes. Brand new JJ all around and I have no more microphonic feedback and all is well.
Hi - just picked up this express 5:25. On the burn channel with my Les Paul studio, with gain maxed out, I am getting tons of feedback unless I run the master pretty low - like 7 o clock or 8 o clock. Is this normal or is something wrong?