[CentOS] yum consumes machine (load average soars to 47)

I was using yum to update packages a few nights ago on one of my servers. The update of rpm packages appeared to die. Since then, commands like 'yum check-update' will consume the system. This is a dual-core Pentium-D, with X64 (and I'm running 64 bit). One CPU pegs at 100% running yum, but whatever it's doing on disk really is the bigger issue. It so consumes the disk subsystem as everything else grinds to a halt and the system becomes unusable (likely swapping itself silly).

I'd really like to get this resovled and apply errata. What I need to know is where to start looking. I've tried a 'yum clean all' but that doesn't help.

Dan