NASA records mysterious sounds 36 km above Earth's surface
 
    Click to Hear   The sound was recorded by a UNC Chapel Hill payload aboard a high  altitude balloon. The balloon was commissioned by Louisiana State  University's High Altitude Student Platform (HASP) program and flew to  an altitude of ~22 miles in 2014       A  NASA high-altitude balloon experiment run by graduate students in the  US has captured some unexplained and strangely complex sounds at 36 km  (22 miles) above the surface of Earth. Known as atmospheric infrasound, these sound waves dip below frequencies of 20 hertz, which is beyond the range of human hearing.