Guitar effect introduces noise if I'm not touching it's metal case. Why?

[btmm]

As the title says, a guitar effect I built introduces a lot of white noise, which goes away when I touch it's case.

I removed the circuit from the case and found the noise also goes away when I hold the input sockets. How do I fix this?

Thanks for any help!

 

[technician]

You need to check that the case (metal presumably) is connected to earth/ground by means of the outer casing of the lead to the guitar.
I have built and repaired lots of electric guitars and this is the most common electrical effect. You probably realize that all of the exposed metalwork (bridge, socket, switch/ control plate etc) are all connected together and then connected to earth/ground

 

[yungman]

Do you mean this is a battery operating stomp box like a Fuzz Face etc. that don't have power plug that plug into the wall. Guitar just plug into the effect box and a coax jack from the effect box plug into the amplifier? How about when you just hold the guitar by the neck where you touch the strings while plug into the effect box? The strings are usually connect to the ground where it plug into the effect box. Make sure you are not using insulation jack.

Do you have a ohmmeter? If so, measure the string of the guitar to the case of the box. Also from the case of the box to the outside of the input jack of the amplifier. They should be shorted as these are all supposed to be grounded. If you find one is open, that's where your problem is.

What do you mean by white noise, usually problem like this is the 60Hz and it's harmonics, not white noise. White noise is wide band hissing sound...like Pzzzzzzz......