Guitar or Computer's Picking up Radio

[Amerikhastan]

Ok, so when I'm using garageband and i have my guitar plugged into my iMac i can hear faintly but audibly hear in the background, music. Now it stops as soon as i turn down the volume on my guitar so I'm thinking that it's picking up radio. So does anyone know how i can get rid of it?

 

[zimv20]

try a guitar cable with better shielding. but that's no guarantee.

 

[ausdave]

Also try using a different length cable (shorter is generally better), but changing the length should alter the radio frequency that the cable picks up.