Hello

I have an ENGL Fireball SE20, with an associated 2 * 12″ cabinet that can run in both mono and stereo. Then I have an EHX Howitzer amp. Now if I put the cabinet in stereo mode and connect each of my 2 amps to the cabinet, they work as intended, individually. But as soon as the two amps somehow connect via the shaft of the jack, the Howitzer emits a clicking sound at about 1hz. It doesn’t matter if my ENGL is on or not. I have contacted ENGL and their first suggestion was to turn the groundloop switch on my SE20 on/off. Unfortunately that has no effect. Both amps are connected to the same power supply which is connected to a ground. There are no other gear connected, just to amps to one cabinet in stereo. Does anyone here have a troubleshooting suggestion?

Sincerely Michael