No one knows exactly how the tradition, known as the Flogsta roar, started, but every night at 10 p.m., students in the Flogsta neighborhood near Uppsala University open their windows and scream, The Local.se reported.
Some believe that the nightly event is just a way for students to relieve stress, others say it started as a way of honoring an Uppsala student who committed suicide in the 1970s.
The howling died down for a while, but was revived by two student radio DJs in Flogsta in 2006 who tried to beat the world record for most people screaming at one time. Flogsta did not break the record, but the tradition was started again.
The phenomenon has now spread to other college campuses across Sweden, including campuses in Lund, Linkoping and Stockholm.