Which type of signals need to be shielded to ground in an effect?

[sjaltenb]

Ok so im about to wire up my entire multiFX box.

I know that using shielded wire and tapping the shield to ground GREATLY reduces my hum and improves the signal quality, so of course, ALL my signal wires will be shielded and tapped to ground. I am using belden 22ga twisted pair for FX signal S/R from the switches and RG-174 for pure signal path.

I also have AC and DC power running through the box. I am pretty sure the AC should be shielded and grounded, but what about the DC?

I will have DC running all around the board to power the FX of course, but also the backlighting LEDs and the indicator LEDs. What causes things like this to hum?

The LEDs for both backlighting and indicators with run at a constant, adjustable voltage from a LM317 circuit. Thanks!