I don't know where the samples come from. This is just a guess, but I would take a wild shot and say that the samples come from some old Roland drum machine of some sort and he distorted them. I don't actually know though. If there was an Aphex Twin Sound Sources Sheet (God I wish there was) I could confirm it. But no, there's not a sheet of that out there. I think...
Help us by donating!
Musical Artifacts is an open source web app helping musicians to find, share and preserve the artifacts they use for music production. It's worked on by volunteers in their free time.