With regard to my question, I guess I was just assuming that if noise gets in before the amp then the amp would amplify the noise too.

Well, yeah, sort of. But you have to understand how ground loops work to see that it's not really a question of where the "noise is getting in". The entire signal chain is kind of like one entity. The power going to the amplifier is indirectly connected to the signal cables, which is indirectly connected to the empeg's circuitry, which is indirectly connected to the empeg's power source. Ground loops occur when the resistance to the grounds at each point varies, causing voltage from the power supplies to leak into the signal chain, hence the pops you're hearing.

And as far as inductive noise is concerned, those signal cables are like a big antenna, picking up whatever's going on around them...

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Tony Fabris