I built two in the clear polycarbonate case.
The first one, I grounded the stomp switch and the pots and used unshielded cable. It hummed even in bypass mode. The hum was sensitive to box orientation, indicating that it was picking up the magnetic field from a transformer somewhere, either the amp or the pedal power supply. I put in coax cable from the IN & OUT jacks to the stomp switch and that cured he hum. I grounded the coax at both ends.
The second one I built, I used coax cable but did not ground the pots or switch. No hum.