Trying to diagnose hum problems

[Longways to Go]

do you have more than one amp, more than one guitar, more than one cable?

if so, it should be easy to eliminate some possibilities.
If 2 guitars produce similar hum, guitar is most likely not the source.
If 2 amps produce similar hum, amp is most likely not the source.
Same for the cables.

Seems to me it would be useful to know if the problem originates with the guitar gear or the house.
No sense fiddling with your guitars if the house wiring is to blame.

[BigToe]

That's not enough of a diagnostic to eliminate the amp; really need to test it with something plugged in. That's why I suggested plugging in an MP3 player to the amp.

I'm not sure using an mp3 player would help deduce the amp being the source of the noise. Using a very low impedance device (MP3 player) into a very high impedance device (guitar amp) might not be the best choice as the two devices are not meant to work together. matching the db level to simulate what a guitar would be might introduce more noise. plus using 1/8" to 1/4" adapters or stereo cables are adding more variables to me.

[vintagelove]

What is the logic behind your theory?

Im not sure what logic is needed, when he touches the strings, the noise is reduced, indicating there is a connection from the strings to ground.