Hi All....
The problem is sorted! My uncle has a garage and made a few phone calls, and an old friend of his came and had a look at it, and charged me nothing! Bonus!
He spent a good hour going round the car, and we found the fault was with the head unit. Im not sure about the technical language, but the generalisation was, that at some point of installation, one of the circuit boards connected to the 2nd pair of RCA`s, had actually fried on the white RCA side-this had actually caused the internal earth in the lead to become inactive. He said its not as bad as it sounded. If i wanted to send the unit back to the company, he said this would not be covered by warranty and i would be looking at an £80+ bill. The alternative was this-he clipped a crocodile clip on to the head unit, and touched the dodgy fried white RCA (which was all wired up to the system) with the other end-and the noise stopped. So he suggested that if i wanted to, i could just use an old bit of speaker wire, put a fork shaped spade connector one end and use one of the screws on the unit to connect it to the body of the unit, and solder the other end to the bare metal outer lip on the RCA, after it had been connected. It was that simple. And it has stopped it. It was also suggested that i could do the remaining RCA from that pair(Red one) and then do the other pair as well, to prevent the problem happening to the others-i just done the one for now-there are enough wires behind the unit as it is. What was the cause then? This was my following question. He said he has done the same thing in the past-its so easily done, and you wouldnt notice you`d done it until you turn the engine on. It could be as simple as two stereo wires touching, turning your amps on, or even pushing your head unit in the slot in your dash-he said he thinks its bad that the problem is still about, specially with all the technology around. So, problem sorted. Oh, and before i got the chap out, i did try a Surpressor, and it didnt make a shits worth of difference! It may not be the same on your head unit, but you could try doing the same to yours. Connect a wire to the metal body of the unit, turn it all on(inc. engine), and just touch the other end on all the RCA`s until the noise goes. If that doesn`t work, then i can be of no more help. It would then be a nice expensive trip to an ICE dealer i should imagine!
Let me know how you get on-cheers for the reply previous to this too. Oh, one more thing-how is the Turbo coming along?

Later, Happy Dan :-)