Tubes can have microphonics, and they are easily measured and heard. Soli state, not so much. P-P wiring does away with PCBs, but the wires can ring - audibly and measurably in a P-P wired tube amp also. So at what frequencies did the micro-resonances occur? You can change the frequencies by mass loading the PCB or you can absorb them by mounting the PCB on Sorbothane.