Why can I hear the cursor flashing on my screen through my headphones?

Question

As well as just about everything else that changes on the screen, from loading a webpage, scrolling a window, typing, moving the mouse around, etc.? I have the headphones on, and I can hear it all. When I try to record a screencast with Camtasia 7, I get a lot of noise in the audio track.

I have an Asus desktop (within a year old). 64-bit running Windows 7.

Thanks for any suggestions! If I need to provide more information, please let me know.

Edit: The noise is like a high-frequency whirr with different high-frequency chirps when the different activities on the screen take place. They're not loud chirps, but I can hear the frequency of the whirr change a bit, if that make sense.

I have a wireless keyboard and mouse. Someone else suggested switching those out with a wired KB/mouse.

Answer 1

It's called Electromagnetic Interference. It's very common with electronic devices, and is usually most noticeable by speakers or headphones, as you have noticed, but can also be picked up by radios, TVs, telephones, or any number of other devices.

You may be able to reduce or eliminate the problem to get a higher quality of headphones--specifically "shielded" head phones. It might also help to use shielded cables for your other electronic devices--like your monitor cable, etc.

Answer 2

A brief summary: I have the same problem, and I do not have the answer. I want to dispute the accepted answer, as a means of constructive debate, as well as provide more information in order to get to the bottom of it.

Just as you stated, the noise comes from anything going on on the screen, such as a cursor blinking. The noise is audible when both mouse and keyboard are not in use (noise persists if the peripherals are switched off). So let's put this hypothesis to rest (switching out mouse/kbd for wired). The noise comes from either the video card or the monitor.

Now, to the quality of headphones. I have a somewhat budget audiophile setup (by hi-end audio standards) that consists of separate components: DAC, preamp, power amp, quality headphones, quality cables (USB, speaker cables, interconnects). Let's just say that each component is no less than 1000$, with some costing way more. So the noise is not due to lack of insulation/shielding in the headphones or any other components.

That leaves us with the sound card (a dedicated DAC in my case). The noise originates somewhere in the video card, then travels via the USB cable, and makes it into the analog stage, despite the assumption that a good quality sound card should filter out any noise.

To test this hypothesis, I am going to do an experiment: connect a digital oscilloscope to various points of signal path, from the USB cable to DAC output. Without any music being played, the "cursor noise" should be clearly discerned.

I will update this post in a few days. In the meantime, I suggest you un-accept the currently accepted answer in order to keep it open and encourage potentially knowledgeable people to post answers.

Update:

The scope was not necessary. Upon discussing the issue with the DAC vendor, it was suggested that I might have a ground loop. Indeed, I reshuffled my cables following renovation of my living room, and ended up with a laptop and a DAC plugged into different wall outlets. As soon as I moved them to a common power strip, all noise disappeared completely.