Story highlights The lockdown was lifted after 90 minutes

University: Student did the right thing

(CNN) A military academy and a university in suburban Philadelphia are locked down. Officers from two police departments rush in to search for a gunman.

The cause: No, not gunshots -- but bubble wrap.

Around 6 p.m. Monday, an Eastern University student called 911 after hearing what she thought was a gunshot.

Police from Radnor and Tredyffrin Township showed up and searched the campus. They found no evidence of a gun fired.

The sound, it turns out, was something else.

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