"Static" noise when brake pedal deployed?!

I don't often read the ICE section of the forum since it isn't high on my list of priorities whilst driving the coupe, however on returning home from Kent Italian Car Day I had the radio on and noticed the repeated incidence of a static 'mush' noise on the radio.
Firstly I thought it was just bad reception but then noticed that it only occurred when I hit the brake pedal.
When back at home I tried the radio and brake pedal with the engine switched off and still the same noise. However with the USB or iPhone plugged in- nothing wrong at all, engine running or not! I have never noticed this before and think it has only just started to be an issue- the Sony radio was fitted about 3 years ago.
It must be some kind of earthing problem activated by the brake pedal going on but I don't see how.

Any ICE supremoes know what could be wrong and how I can fix it?

Your wiring at the back of the radio I suspect will be chafed. It will either be something physically catching around the brake pedal, or more likely just a wire that shares potential with the brake switch.

Have you had any fuses blow lately?

Well worth investigating the wiring behind the radio and following it round to the dash. Common coupé problem that has potential to cause a fire.

If the noise is only when your using the radio I would start with the antenna lead, maybe it has worked loose or dropped down near the brake pedal.

Check the earths at the rear of the car, there's one below the n/s/r lights, under the plastic panel/carpet, and it could be that the aeriel amplifier earths there. A classic sign of a poor earth at the back of the car is if you have the side lights on and you press the brake pedal, the rear light/brake light goes off, then comes on again when you lift off the pedal, since the side light is finding an earth via the brake light circuit. You may find you get interference also when using the heated rear window, which again is probably earthed at the same point. Using anything else (HRW, brake lights) that shares the same earth as the aeriel amplifier can cause these problems if the earth connection to the body is in poor condition.

Edit: It looks like all the rear lights, wiper motor, fuel gauge share the earth under the n/s/r lights, but the HRW has it's own earth on the C pillar. The radio itself is earthed at the front, but the aeriel amplifier seems to earth via the aeriel itself, I can only see a power connection?

Anyway, check the earths!

Have you checked you front brake pads? If the wear indicator is just starting to touch it can cause this sort of interference even if the wear indicator bulb is not lighting.