Radio problems

OK, the whirring in sync with engine speed is commonly an alternator whine. Since it went away when you disconnected the field, that seem to point to the alternator pretty conclusively.

Try this: run the car at night with the lights on, and see if the headlights dim more than usual when you drop the car to idle. I have to wonder if a diode is gone in the alternator, causing a lot higher than normal AC ripple on the output that is causing the whine. When you lose a diode, then the lights will usually dim more than normal at idle. The battery charging will also be weak.

You might also want to measure the battery voltage when running at fast idle and normal idle and let us know the readings. It might give a clue.....but might not.

Is the suppressor at the radio or at the alternator?