thanks faranks, that's an interesting suggestion, i will try that and let you know if that works!

its actually not the low level output from the head unit but the high level output from the amp that i'm taking. i think its probably different to what you may see in the US, in europe , its a BM54 amp which is located right next to the battery.

wiring i picked up is as in below (2002 radio module with nav)
http://www.xoutpost.com/articles/x5/...formation.html.

but interestingly my colours were slightly different (probably cos this is teh european model):
blue/purple, blue/gray: right rear
yellow/purple, yellow/gray: left rear

i will try your suggestion tomorrow. at the same time, any other suggestions you can think of please, like adding a resistor, or capacitor to the line, etc, to kill the noise?

cheers

j