Assuming your VVR circuit is working correctly... I can't tell you why or where, but it sounds like a classic preamp or phase inverter oscillation to me... probably your "cleaned up wiring" has created a positive feedback to a preamp stage... I'd move some wires around like they use to be just to see if anything changes.. and I mean the frequency it buzzes or the intensity... etc.
As it is now.... that is a BUTT load of gain for couple EL84s!!
Is it the same with the low gain setup as the high gain, or worse with one?