1 stratman 2 years ago I have a digital reverb pedal that was apparently causing unbearable hum. It only occurred when the pedal was engaged, otherwise the hum was gone. My first thought was that it was the pedal itself - seemed pretty obvious. However, after a while of troubleshooting, I determined (I think) that it was the cable that leaves the reverb pedal and returns to the amp. Otherwise, the cable works fine. I swapped it with a different cable and the problem seemed to disappear. A cable is pretty simple - two conductors. What could possibly cause an otherwise good cable to inject hum into an effects chain, and only when the one pedal is engaged? I'm stumped.