I recently got a SM57 mic and wanted to record my guitar amp. I have a Fender Frontman 25R. The mic is plugged into a Scarlett 2i2. I'm recording via GarageBand. Unfortunately, in a barebones signal, there appears an obnoxious humming!
The humming is definitely caused by the amp because when I turn it off it disappears (there's still a hiss but that probably won't make it through the mix especially if I add a touch of EQ-ing). It's definitely a bad cable or pedal cuz nothing is plugged into the amp. It happens regardless of whether the amp is plugged into the wall outlet directly or through a power strip.
I've read that "ground loops" can present a problem but I'm not exactly what the loops in question are. The Scarlett 2i2 is plugged into a USB hub whose power cable is plugged into a surge protector into a different outlet than the amp... it's a lot of connections I know but this is part of my apartment desk setup rather than a dedicated studio.
What could be the issue here? Is it a small fix or am I screwed by virtue of having to record in my apartment? If the issue is insurmountable I might have to return the SM57 and stick with just a DI guitar signal and the amp sims in GarageBand :(
Edit: I forgot to mention but the humming is only heard at the end of the SM57 -> 2i2 -> GarageBand chain. I don't hear it directly from the amp with my ears. So either it's non-existent in real life and is induced into the signal chain, or it's present in real life but it's super faint and is amplified by the signal chain. The former seems more likely.
UPDATE: The issue occurs even when my laptop and the 2i2 are powered by the laptop's battery rather than a power adapter plugged into the wall.