I have an ASUS VS248 Monitor that seems to be producing a faint beeping sound in my headphones when I have the monitor turned on. When I turn the monitor (only) off, the beeping mostly stops. So I'm fairly sure it's got something to do with interference from the monitor.

I have a PreSonus Audiobox USB external soundcard that I use with KRK Rokit 5 speakers. The beeping sound may also be coming through the speakers, however I can only notice it through my headphones (due to the noise cancellation of the headphones). I can't really seem to notice the beeping while listening to music, but at times when I have no sound coming from the headphones, it becomes quite annoying.

The beeping sound is a faint low pitched sound (square wave type sound) followed by a slightly higher pitched beep (of the same sound) 5-6 seconds later. This process repeats. Sometimes the beeping will be rapid (BEEP BEEP BEEP).

I have tried the following without any luck of finding a solution:
- moving the USB cable (going from the audiobox to the back of the PC) away from the monitor and monitor cables
- moving the actual soundcard (box) away from the monitor itself
- removing my wireless keyboard and mouse usb from the back of my computer
- removing the microphone and audio inputs/outputs from the sound options in 'devices'
- plugging the monitor into a different power point
- changing the brightness and contrast of the monitor
- changing from HDMI to DVI monitor input
- removing the wireless adapter at the back of the PC
- changing the usb ports used for the external sound card

Anyone have any ideas? Thanks in advance.