I'm having the identical problem with a bunch of 5 new P5440FA laptops.
Grey lines flickering across the webcam video image in Teams and Zoom and in the Camera app itself.
The disturbance seems to be mostly linked to use of the mouse during the session, both through the trackpad or an external mouse.
Updating the BIOS from the .303 version that came with the laptops to the latest .308 version makes no difference.
There is no disturbance if AC power is unplugged.
I notice Blake_ASUS that are also dealing with what appears to be the same issue (but running since December) in a separate thread at
https://zentalk.asus.com/en/discussion/20761/grey-lines-and-green-flicker-on-webcam-when-using-ac-po.... It would be helpful to know whether this is actually something that can be resolved or whether it is essentially a wiring fault in the laptop that cannot be fixed.