more switch pop questions and some new revelations

[tempus]

Hey all;

A while back I built a switching matrix to switch my fx pedals in and out of the signal path. It's driven by a PIC, and the switching is accomplished with JFETs. Switching should be dead quiet right? Well, it almost is, except for kind of a "thump" sound whenever I switch anything. It's barely noticeable, but I figure I should be able to get it completely silent, so I've been living with the noise but keeping my eyes open for a solution.

I discovered something last night that might help me (and others hopefully) to solve these pesky switch pop problems. I've got a piezo bridge in my electric guitar which allows me to get an acoustic sound from my electric. Both my piezo and magnetic signals go into the board and are kept separate by an Ernie Ball stereo panner. The piezo sound goes from the panner to a Zoom A2 acoustic multi fx unit, then through a transformer to the PA. The piezo signal never gets switched; the A2 is not in the loop I described above, which is strictly for my electric guitar effects and goes out to my amp. However, when I push any of the switches to switch fx in the switching matrix, I get the same thump sound in the PA! How can this be? I always figured that my switching noise was the result of the effect being switched in and out, but since the piezo is not even in the switching signal chain, it must be something else. Could it be a power supply issue? It's not in the schematic, but the whole thing is powered by a 500ma wall wart, which feeds a 9v regulator (for pedals) which feeds a 5v regulator (for the PIC).

Any ideas on this one? Here's the schematic: