I like that user name, so I assume you have a rat-rod...?
Back to your question - two thoughts:
Is there any chance that your AC line and your 20 amp Eq feed might somehow be sharing a neutral line from the breaker box - hopefully not.
As for moving that breaker to the other side in attempt to separate - please keep in mind that a 220 central AC unit is pulling from both sides.
I would next be thinking about the "rush-startup-input-surge" occurring when the AC starts up > momentarily adding some ground noise? Any chance your 20Amp EQ feed is on a dedicated ground, or could it be converted to a dedicated ground? I would start thinking about testing for ground noise