Tnx Tony for the link. I'll investigate further here.
Les: I already did this by using a separate power supply and shutting down all other equipment.
I have all my equipment connected to 230V and 12V power supplies. the system here is not directly connected to the house mains as I use an isolation transformer and a dedicated radio ground.
The additional clamp on ferrite didn't have any effect unfortunately.
Getting complex now....
