Get Jack running with RT priorities to an external USB soundcard (I'm using
a Lexicon Omega). Then do a big apt-get dist-upgrade or something which does
a lot of IO - bonnie++ will probably do it. You'll get sound skips. And
this isn't on poxy systems - I'm on a Quad Core, 2.6GHz, 4GB RAM and
(software) RAID 1. Heavy IO just kills low latency audio.