Simplex 4100 Audio

I have a supervision tone bleeding over onto some speakers on a Simplex 4100 system. It disappears when the audio cable is removed from the audio card and or when some of the audio riser cables get disconnected. I suspected maybe field wiring causing induced voltage or internal board issues but went through all the speaker circuits in the field and everything was ok. I noticed the tone is only faint on some circuits but louder on others.

Would like to find a wiring diagram for the 562-905 25 watt amplifier cards so I can verify the riser wire and cables feeding the amps are wired correctly. Any Ideas or diagrams that could be shared would be much appreciated.

Or information on possible cause?

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