The Longfellow Boom is a loud and unexplained phenomenon reported in the Longfellow community of Minneapolis, Minnesota, United States. The booms reportedly generally take place on summer nights, and have been described by residents as "house-shakingly loud" and at lower tone, distinct from a car crash or gunshot. Those investigating the booms believe they are mostly likely caused by several types of unrelated human activities, such as fireworks and improvised explosives being lit in the Mississippi River gorge, trains decoupling, and cars backfiring.