Just listened again using my headphones. So hard to tell over the hoover noise (next time you record ask your mum/wife/gf/whatever to stop hoovering for a minute).
However..
The noise sounds like resonance (I think that's what it is called). I've had this where a hard drive was vibrating at a certain frequency that resonated with something else in the case, or perhaps the case itself. To fix it I stuck a wedge under one side of my case, and eventually suspended the hard drive. The hard drive itself wasn't noisy when isolated from the case but the noise it created together with something else was 3 or 4 times louder and going up and down in volume.
I also had it with my stock reference HD6950 cooler which made a up and down thrumming noise when I sat in a certain vector from my computer. For the 6950 I just changed the cooler as there was nothing else I could do and besides it was too noisy anyway.
This sort of noise can be caused by a fan with a worn bearing, where a certain amount of vibration occurs at a certain speed of the fan. Something is tuned into it and both make a noise when it hits that speed. You should be able to adjust the graphics card fan speed manually until you find the speed with which it occurs. If it's the CPU fan then you can also test this.
I doubt if this is electrical noise.
It's often hard to find the cause of these things as the noise doesn't always come from the part making it, if that makes sense. With my hard drive I thought it was the rear fan until I put my finger on it and felt it's vibrations in tune with the case.
Good luck.