what is a tech going to be looking for in my rig?
This is not a topic we can handle here – many times it's a matter of trying things and fiddling about. Often comes down to experience.
Power supplies are not usually the problem, as they are not normally grounded. Use the Eventide ones until you have resolved the other problems.
Make sure (as you mention) that everything is grounded to the same outlet.
Then it's a matter of connecting and disconnecting cables until you get a feel where the problem lies.
When you find one that when disconnected, fixes the problem, try just touching the casings of the jack to the ground of the connector and see if that brings it back. If it does, consider lifting the ground to that jack.
But, why this needs someone who knows what they are doing is that removing grounds can leave the setup in a dangerous state. Quite a few musicians have been electrocuted in this way, so you are working at your own risk.
When all is working OK, go round with a testmeter, and make sure that you have continuity between all metal surfaces. This should give you a chance.
