Are you able to run the amp in a 2 input, 4 output mode? Might just be worth doing as a test that only takes a couple of minutes.

I've just skim read the post so apologise if this has already been addressed -

Have yo routed your RCAs away from any power cables? That is usually the problem.

RCAs down the centre, speaker cable one side and power on the other.

HTHs

Nick.

I dont think so but I'll go have a check after a bacon butty.

Yep, RCA's are now down the transmission tunnel. I tried them across the top of the car and bootlid to get them away from everything but that didn't work either.

I've tidied up the amp install too this morning and mounted it on a piece of MDF in the spare wheel area so I have all my boot space back and managed to give the car a good wash before the rain set in. :)

not tried the rca twist idea. im using a 2ch amp and getting noise.
i've given up trying to diagnose :p spent half a week trying to get it sorted.

weirdly, it only happened once i plugged in either the active cross-over or tweaters (i forget which). ofcourse, tweaters might just of highlighted the issue as it's likely to be within their frequency range.

FIXED!!!

Cable worked like a charm!