Home Studio Hum Mystery — Could It Be My USB Interface?

[ignatius]

I’m new here and just getting deeper into producing my own tracks at home (mostly indie pop and ambient stuff). Lately I’ve been hearing a low, persistent hum in my recordings — it’s faint, but definitely there in both vocals and instrument inputs.
My setup:

• Scarlett 2i2 (3rd gen)

• Rode NT1-A mic

• MacBook Pro (M1, 2021)

• GarageBand (I know, I know — planning to switch to Logic soon)

The weird part: the hum disappears when I unplug my laptop’s charger, but I can’t run long sessions on battery. I’ve tried switching outlets, different USB cables, and even using a power conditioner, but no luck.
Could it be a grounding issue with the interface? Or something else I’m overlooking? Would love to hear if anyone here has dealt with something similar — or if it’s time to upgrade my interface.
Thanks in advance!

[AlanHall]

The weird part: the hum disappears when I unplug my laptop’s charger

Not weird, but important!
does the hum go away when you [answer either A or B]
A) unplug the charger from the line (wall socket) with the charger still connected to the laptop, or
B) unplug the charger from the laptop with the charger still connected to the wall socket?

if A, then the charger (SMPS brick) is radiating EMI into your system. Try repositioning the charger or plugging it into a different outlet.

if B, then the charger is inserting digital noise (common with many SMPS units) into your laptop, where it propagates to the sound card and you hear the digital 'hash'. The solution there is to look for a less noisy charger.

Note: this is not an exhaustive list of things that could be wrong, just a first iteration of troubleshooting. Hope this helps!

[cosmicdolphin]

Sounds like a ground loop