gjhome,
My apolgies for duff gen, I don't have a 525 to play with at the moment, however I have discussed this with my avionic collegues, we believe that if the avionics are OFF you do not recieve voice warnings through the speaker, however you do recieve through the headset.
If the aircraft is N reg you do not require to have voice warnings, however G reg aircraft do. If your aircraft is N reg you can ask Engineering to disable the voice warning by selecting the switch on the back of the annunciator panel.
We think that checklist 69 has the correct answer re the squelch, next time we have a 525 in the hangar we will look at this and report further.
Best regards,
om15