Extremely noisy audio when both PG Express and monitor are connected to my MacBook

[theriverwards]

Hi, I just took my new Pod Go Express Bass out of the box tonight, and when I connected it to my MacBook Pro to use Pod Express Edit, there was a significant amount of hum/interference in the speaker I was connected to. When I unplugged my external monitor from the MacBook, it disappeared. I'd be grateful for any suggestions about how to overcome this.

 

I have the Express unit sending audio via a regular patch cable to the unbalanced input on a powered PA speaker (JBL EON15 G2). The data connection is a USB-C to USB-A cable into a hub that goes into a USB-C port on the computer (though it wasn't any better when I went USB-C to USB-C directly into the computer's port). The monitor is connected via an HDMI to USB-C adapter into USB-C on the MacBook.

 

Thanks!