Yesterday I decided to go to Blair and see how one of their Thunderbolts are doing. The one I went do isnt doing so well now. Here is today's video: https://www.youtube.com/watch?v=2WtM3CWDrYU:
The wind up sounds interesting, you can hear how badly it fluctuates, its going down hill. Here is a video from 2010 of the same siren: https://www.youtube.com/watch?v=lfnGdJ2-Cy0
And before the "siren expert kids" come in to state the obvious. Yes, it needs new bearings, along with brushes and rings checked.