First thing to try is to check the grounding and change the ground to
another point in the car for both amp and head unit, this should resolve the
problem but if it doesn't pick up a ground loop Isolater from maplins(costs
about £8) for the phono leads. I had exactly the same problem and the ground
loop isolater has got rid of the interference.

Ritz

"news.gxn.co.uk" wrote in message
...
Hi,

I've just installed a Sony Cd head unit, and Sony 4-way amp driving two 7
x
10's on channels 1 and 2 and a sub which is bridged across 3 and 4.

The head just drives 2 100mm units in the dash

Systems sounds great on both CD and Radio but when I switch on the engine
I
get a high pitched interference which varies in pitch according to revs,
regardless of the source (CD or Radio).

My question is what causes this interference and how can I kill it ?

TJ