It may seem silly and not work but check the volume control on the mic pocket to make sure it is not up. Even with nothing plugged in but the volume up on the mic input any noise generated by interference may be getting amplified. This would be rare and only likely if the mic was getting interference from a
speaker lead.
Do you have the wiring diagrams for this setup. I take it you have some form of programmed audio distribution
system do you have the correct list of what each
button is meant to do. Has anyone reprogrammed it lately? Was there a test
button included to
send a test tone through the
system eg 1KHz. Does the
feedback occurr as son as you
switch the speakers on?
Does the
feedback go away when you
plug anything into the mic /
line pockets.
I would start by checking the
system diagrams.
But also I would start pulling cables out starting with the amplifiers.
Pull the input leads out of the amplifiers and turn checking for
feedback.
Then
plug the leads back in
feedback still there?
Disconnect the leads to the
amplifier at the end furtherest from the
amplifier check for feed back.
Keep working this way back up to the mic /
line pockets this should isolate the problem.
Double check any signal processing equipment that is connect after the mic/
line pockets for any test signals any one might have accidentaly turned on.
A more detailed list of every piece of equipment in the audio chain with make and model number may help us to help you.
