musique concrete, as originally described by pierre schaeffer, was originally supposed to describe aural ideas expressed through the manipulation of tapes. with the Nazis' invention of the magnetic tape recorder during the war, and the subsequent marketing of the technology in the few years following, schaeffer's ideas began playing sometime near 1948 on an egyptian radio station, if i remember correctly.
the nature of musique concrete is that while it was originally based on found instrumentation, the invention and subsequent exploration of synthesizers allowed for an incredible amount of sounds to play with. early composers attempted to utilize popular compositional techniques - particularly serialism - to allow for some form to their creations, but for the most part it really was just playing around with sound - similar to early composers playing with ideas outside the traditional bounds of tonality and the church modes.
if you want an example, there's a myriad of stuff out there that really fits this genre, but i'd recommend mario davidovsky's pulizter-winning synchronisms no. 6, for piano and tape. it's hard to listen to unless you've got a good explanation for what's going on, but it perfectly demonstrates these concepts. if you want something more 'found', schaeffer's early works would suffice, i'd think.
since this youtube example's got a lot of pitch-shifting and all that, i'd say it qualifies as musique concrete. the use of various effects, like tape delay, stuttering, and timeshifting, kind of give that away. if it's just banging on doors and stuff, though, it's not really musique concrete. there has to be that manipulation of timbre and time to really give it that name.
i did a lecture recital on the music of jacob ter veldhuis, and he was profoundly influenced by traditional musique concrete, particularly in his works Billie and Pitch Black (both of which are highly listenable, and really cool works for saxophone/sax quartet and tape). i also did a term paper on synchronisms no. 6 =)
did that help?