Unfortunately, no luck. I purchased a quality line conditioner from APC, no effect whatsoever, except that connecting it to the Pinball machine caused the coils to be much weaker - the ball isn't fired at nearly a high speed. I tried connecting the line conditioner to the speaker. No luck. Tried surge protectors on everything. No luck. Tried surge protectors WITH line conditioner. No luck.
A musician friend suggested lifting the ground on the speaker. Since it's high up in the air, I'm not worried about getting zapped from it while touching a microphone... I'll report back.
EDIT: Forgot to mention, the pops stop happening if I disconnect the XLR (sound in). I believe this means that the interference is happening through the XLR cable, not the power. This makes sense, as a power conditioner wouldn't halt any EM interference through an XLR cable. I don't have, but could purchase one of those anti-hum boxes, but lifting the ground should probably give me the same effect, as believe that those anti-hum boxes are ground-loop eliminators.
Post edited by nbolmer : update