The sound that sparked a lockdown at a suburban Philadelphia military academy was most likely caused by bubble wrap being popped, and not gunfire.

Officials with the Valley Forge Military Academy and College say a student who lives in an Eastern University apartment building located on the academy's property heard what she thought were shots fired Monday evening, and called 911.

Police from Radnor and Tredyffrin Townships responded, and the academy, Eastern University and nearby Cabrini University were all placed on lockdown while police searched the area.

They found no weapons or evidence of any weapons being fired, and no one was injured.

The lockdown was lifted about an hour and a half later.

Officials say it's believed the sound the student heard was bubble wrap being popped.