Gnd != 0V

I hate grounding issues. Almost as much as I hate unconventional
schematics and nearly undocumented circuit-boards. Naturally they all
appeared together. In the end one wire and one cut track gave me an
order of magnitude improvement in output noise for the old piezo
driver, but it took three days to figure out which track to cut and
where to put the wire. Remember boys and girls: never run your power
supply ground through the same bit of copper as your signal
grounds (and always document the circuit-board).