Use TRS or XLR - they have 3 sections +, - and ground, as opposed to a guitar cable which only has 2.

What happens with TRS and XLR is that the sound signal is sent twice - on the + and -. Only the sounds which are identical on both the + and - get used - any additional noise coming on either channel gets dropped. Therefore, any interference which happened on the way, gets removed.

Also remember that a long copper wire makes a great antenna. Antennas pick up lots of noise and frequencies. In essence, a sound cable is essentially that. Therefore if you want clean and honest sound - you gotta use balanced (ie TRS or XLR) cables.

Chony