I'm getting a hum and here is the setup. I've been playing with two amps for years. I just recently picked up a Marshall Vintage/Modern. When I plug in the two amp setup with the Marshall, I get this loud hum. I swapped out the Marshall for another amp....NO HUM. What's up with this? I've checked all cables and made sure they are plugged in to the same power supply to avoid a ground loop. All tubes are good. And, I've also taken out pedals that are in the path.
Any suggestions would be greatly appreciated.