Garageband Buzzing w/ Mic
So I just got a new mic (Rockville RCM03 Condenser) but it has one of the headphone circular jacks I'd have to put into the headphone port, so I bought a USB sound card to connect the mic to my Mac Air. I also use headphones and plug them into the actual headphone port so I can hear things, but whenever I plug the USB into the computer with the headphones when using Garageband and turning on monitoring, this buzzing sound comes on. I think I've literally tried everything from noise gate to feedback reduction to switching the physical plugs and the plug-ins, but the noise is still there. I'm starting to think it's the mic or the USB because the sound isn't there when I take the USB out and listen with my headphones. Please help
MacBook Air 11″, macOS 10.14