Thanks guys,
The connector to the SAT board was missing a ground.. have made a new connector, but this still has not fixed the whistle.
The grounding on these 2 boards is very suspect... once again piss poor design... it leads to all sorts of interferance, i can change the tone of the whistle by placing a finger on a cap and also change the level of noise through the speakers by moving connector wires.
The original cables were braided and run to ground... might be worth putting some ferrite rings in line
