My only suggestion is a real degaussing wand. Failing that, if you have an old TV you can make one.
Remove the degauss coil from the tube. Round it out as best as you can.
Grasp each side with your hands and twist it into a figure eight. Then fold it so it's a double circle.
Use 4" wire ties to tie it all together.
Cut the plug off the end, and bare the wires back about two inches. Get a lamp cord. Leave the plug end, bare the other end back about two inches.
Wrap each wire around the other - eg wrap one end of the lamp cord around the degauss ring.
Now solder it up so it's not going to come apart.
Wrap it WELL with electrical tape. Triple thick.
Obviously you don't want to just plug this into a wall socket - there's no switch and it will get hot quite quickly. Get a power strip and plug it into that. Since it has a power switch you can turn it on and off quickly.
Wear gloves. Not for the shock - it gets HOT. FAST.
Hold the unit in one hand, the strip in the other, with your finger on the switch. Do the regular degauss thing. Repeat until clear.
Of course, it could be the position the cab is turned. Have you tried moving the cab 90 degrees, or at all? Give that a shot.