Digitallandfill.co.uk will contain in total 82 short audio loops. Download them, and use them to make your own audio track, add as much of your own sound as you like, as long as you respsect copyright laws (see the legal bit below). You may mess around with the loops themselves too as much as you like. Be inventive and interesting. Go nuts. But don't just slap them on top of your demo tape, that's not going to impress anyone.
I'm not really sure how these guys are affiliated with Radiohead but I guess I don't really care either.