Thanks Guys,

I can confirm that the Amp is wired directly to the battery terminals while
the head unit is just wired into the main loom as normal in place of the old
head unit, is this incorrect ?

I've made a brief check through the system..

The RCA signal leads run from the rear of the head unit and are routed back
to the amp without passing any power leads on the way.

The amplified signal leads which run from the Amplifier to the rear L/R
speakers are routed through the vehicle and are not pinched at all but are
pressed quite tight in places would this have any bearing on the
interference ?

I hope to find time to run right through it again in more depth over the
weekend.

Cheers

TJ