People have reported "noise" on mouse movements or screen redraws that have turned out to be digital artifact due to dropouts as these operations taxed the system, but that would not seem to be plausible if the noise is happening on recording an empty input to a blank project. I assume you are not using a wireless mouse, but it might be worth trying to use a PS2 connected mouse if your motherboard has a socket for one or a USB mouse if you are using PS2 or serial (ancient) connection.
 
The clocking symptom might indicate something in the computer, but two seconds is an eternity in computer time. One thing that springs to mind is an intermittently illuminated neon sign in the area, or a traffic signal. These need not be in close proximity to or connected to the wiring to your computer to cause a problem as they can act as a broadcast source. Unfortunately a lot of intermittent sources of interference do not do anything as noticeable as flashing a light, but it is worth looking around for a device that might be showing this temporal pattern.

Long shot but if I have an input channel unmuted which has phantom power going through it, I get pretty weird noises that end up on my recording. Might be worth checking all your unused inputs are muted?

Hello. I'm having the same problem since I had to replace temporarily my Kronos with a Numa piano. I think that  it's related to the electrical shielding. When I use my wireless trackball upon the Numa I can hear the noise. If I mute the KYB audio channel the noise disappears. Don't know if can help...

I just wanted to add encouragement or a sanity check to this discussion.

I've dealt with noise from various contributing sources over the years. There were times that I thought I couldn't lick a particular issue and settled, accepting that as the fate of my setup. But through persistence I did eliminate them all.

I think it's helpful to know that "normal" for a recording setup can and should mean no noise at all. No hum. Just no sound unless you touch an instrument or play back something.

It can seem acceptable to live with a hum or other noise, but it's a helpful sanity/reality check to hear from others that zero noise is possible and should be normal if you can get there.

Interesting.....I take it that your PC is a tower???? If so....try disconnecting CD drive power....any slave drives.....less likely a floppy drive
 
Are there any Cell phone repeater towers in close proximity to your location....

I've heard this with a wireless mouse (as mentioned above).  I only use a corded mouse now.

Do you live in an apartment that may have something on the other side of the wall that you don't know about?

 
I wouldn't go disconnecting ground wires on electrical equipment, ie the third prong of the mains AC supply, especially in the UK with your 240VAC lines.  The ground is there for a reason and disabling it puts your safety and the safety of others at risk.
 
I agree with what Bristol Jonesey suggests.  Does you computer have onboard sound ?  If so, I'd start with just Windows sounds, onboard sound and your monitors.  If your monitors are powered, try them on their own completely disconnected from everything else.
 
 

Yeah - you have to start wading through the path and try to isolate its origins.  Ungrounded kills.
 
Bob Bone
 

As described this is repetitive and consistent.
Has to be a timed source.
Some control signal, ping, testing for a condition.
(Capacitor charging/discharging?)
Network adapter checking for connection
software updates,....
 
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Reference: my powered speakers do NOT have a third rail on the plug.
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Had an issue a couple of years ago with a static sorta noise. Did all the stuff I could to isolate. Finally called the power company. First thing the dude did was pull out his very big screw driver, open the mains box and tighten the biggest screws, and walla.