Whooshing Sounds Reported Over Granbury, TX

I received these emails from a concerned witness in Granbury, Texas.:

Noise in sky over Granbury this morning May 17, 2015

Any idea what these repetitive whooshing sounds are?  Occur approx. every 4 seconds

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Repetitive whoosing sounds in sky over Granbury, Texas
May 17, 2015
"Sheriff's dept. and fire dept. investigating sounds in sky over Granbury, Texas.  Occurring approx. every 4 seconds.  Any other reports?


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So far no reports have come in, other than this.  If you heard the sounds or heard anything about it, please contact me.   Thanks!  ~Sunny

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