[erdos4d]

How is your desktop connected to the switch (ethernet or wifi)? If the computer is wired, maybe you have a virus on it and that is somehow using the wifi to get another IP? I would suggest you backup your user data and wipe/restore the desktop. If it comes back after that, I'd bet someone has cracked your wifi password and is getting in that way, or some other device on the network is the culprit and reinfecting your desktop.

[wasipwned]

Ethernet, and wifi is disabled. But even if it was wifi or another network interface getting the IP, I should have been able to find it in ip a / ifconfig I'm assuming

[erdos4d]

Maybe I misunderstood what you wrote, but you feel the traffic is actually originating from your desktop? I am completely unaware how someone could get 2 IP addresses for your desktop without that showing up somewhere on the box (agreed, you should have found it with the tools you ran). I still think wipe and wait, but this seems like you got seriously hacked. Good luck.

[wasipwned]

I probably am mistaken that it's originating from my desktop. It is entirely possible that it is multicast traffic I am seeing.

See https://news.ycombinator.com/item?id=33821387