Some sort of power issue. The extra load could be causing noise on the power to the devices. These are incredibly hard on owners that don't want to swap in other parts or another PC. If this was mine I'd have my oscilloscope out to watch those power lines. Also I know to not get stuck with just one camera so I'd test with another.
Hi. I currently have a dynamic mic running through a Line 6 UX1 digital audio interface (it's old but still works perfectly!). The mic gives me crystal clear audio basically all of the time except when I turn on my Logitech C920 webcam. When I turn my webcam on, I can hear my mic start to crackle and snap randomly and if I use it on Zoom or to record something my audio just sounds like TV static. I think it's a bit odd that my mic only stops functioning correctly when my webcam turns on. Is there some kind of compatibility issue or other issue I don't know about that is making my mic sound so bad? Any help would be appreciated. Thank you.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic