baka Grounded Cables.
+1
- check your cables (instrument cables, patch cables)
- check each of your pedals (input and output, pots, switches)
- check your psu (dc cables, AC plug, etc)
- check your guitar's electronics (pup wires, tone and volume pots, input jack, pups)
- lastly, the electronics of the room where you use your gear must be grounded too. have it checked. (AC electrical socket and electrical layout)