A fan archivist has uploaded two rehearsal videos from System Of A Down circa 1998 to YouTube. The System Of A Down Live Archive specializes in "archiving System Of A Down related live material in lossless quality," and invites fans to check out the archive by asking, "Looking for recording of a specific show? You'll find it here!" These two rehearsal recordings each have their own description, which you can find below.
The first rehearsal was filmed before a System Of A Down show in Sacramento, CA on December 11, 1998, while the second was filmed one day after. This puts the band about six months out from the release of their 1998 self-titled debut album. Interestingly if you look at the setlist from the band's December 11 show held at Bojangles, they did perform the Toxicity track "X" that wouldn't surface until 2001!