Well I have fixed the problem.

Bought myself one of those amp wiring kits, came with the 8GA wire for power and earth, and 2 sets of RCA cables, installed it, and now sounds wicked!

Thanks for all the suggestions guys.

whats all this about power cable size and different fuses!!! ok the inteferance is either in the main power to the HU and or amps, or it is in the audio signal going to the amps. no one picked up on that he said its only one amp doing this. a quick test to narrow it down to power to the amp is to disconnect the RCA leads at the amp that is buzzing if the noise goes its NOT the power to the amp. next test is to connect the RCA leads that were going to the buzzing amp and connect them to the good amp, if it buzzes now its either a faulty RCA lead or a faulty line output from the HU. and to doubly make sure its not the amp at fault connect the RCA leads from the good amp and then connect to the buzzing amp. Its probarbly only a faulty RCA lead and not fuses, spark plugs, extra sheilding, noise suppressors...better to find the fault instead of covering it up..