[Tweeters] Anna's vocalization or wing noise?

[Ed Swan]

For about the last month I have heard a single sharp whistle call note with no new bird to account for it when I've tried to track it down.  It happens once and then usually it will be at least half a minute to a minute before I hear it again and I'll hear it two to three or four times before it stops. Earlier this week I heard the sound twice when our Anna's was doing its display.  Could this be the source?  

Ed Swan
Vashon Island
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