The Siren Board

Sounds horrible.
Take it apart and see what's making the noise.
Simple as that.
It would have taken less time to pull the chopper to see what the noise is than it took you to make the video and upload it.

That does not sound good. Here are my guesses to what the problem might be.
1. Bearings need replacement.
2. You might be missing one of the pins which keeps the chopper cap aligned with the chopper.

Sounds like bearings. The brushes send electricity to the chopper. When you had no power the squeaking continued. Mine sometimes hum if it doesn't get a good run every once in a while...
EDIT: But I'd recommend investigating it before you run it again.

The bearing is rusted.

This could be:
The brushes should be able to move a bit because they are on a spring. It seems they are pressing hard on the communicator, which ruins them.
I would suggest not running it and sending it to repair.