Check if your PC / monitor are using a grounded AC outlet.
Find a situation when you hear the static.
Unplug the monitor audio input from the PC and check if it's still audible:
- if it is, then it's related strictly to the monitor;
- if not, it may be related to an interference in the audio interface / motherboard or the cable is improperly shielded
Try to move the audio cable away from power / internet / phone cables.
Try to use headphones and see if the static is still audible.
All the above steps are to be tried when you are sure static was present.
Having a modem / LAN interface right near the (most probably unshielded) audio interface may also cause interference. Also, driver / software issues are not to be excluded.
Please inform us of any findings.