The 6000 Series is a fleet of Washington Metro railcars built by Alstom and placed in service beginning in 2006 for the Washington Metropolitan Area Transit Authority. They became a familiar sight and sound across the system, working alongside older series on busy commuter routes. Rail fans have recorded their door tones, acceleration and station ambience for years, sharing clips on video platforms and soundboards. Those recordings helped turn a routine transit sound into a recognisable reference for DC Metro enthusiasts who can identify the series from its tone alone.