@jasonsf 

This might just be an electrical fault like noise creating random 1's and 0's. 

Is anything plugged into that port?  Can something be plugged into that port for a period of time to see if the spurious MACs stop appearing?

  @d0ugmac1 There is an old unmanaged switch with a handful of devices plugged like a printer and solar panel uplink. I can try unplugging that stuff and see if it changes anything. Worth a shot. 

  @d0ugmac1 Great advice! It looks like I might be able to blame a new usb-c hub we got for my wife's computer. Unplugged the ethernet cable from it and seeing what happens. The hub also gives some audio static on her usb-c headphones and the HDMI monitor on it is flickering a bit- a good indicator that this thing is a cheap, poorly designed piece of Chinese hardware.

  @jasonsf 

Hi, I'm a little curious, did you find the issue?

Is it because of the usb-c hub?

  @Virgo It does appear to be the usb-c Hub. But it happened with multiple usb-c hubs. Oddly, an old usb-A Ethernet adapter wasn't causing an issue. Because my wife needs the hub for HDMI and usb-c headphones, she is keeping it. As long as the Ethernet cable is plugged in to the the usb-a hub, which is then plugged in to the usb-c Hub, there is no problem. It only happens when the Ethernet cable is plugged directly in to the usb-c Hub.