[Hampshire] Phantom CDs on Gutsy

Hi All,
I'm running Kubuntu Gutsy Gibbon.
Ever since I upgraded I've been experiencing a bizzare problem by which
KDE tells me that I've put a CD in the drive (sometimes an Audio CD,
sometimes a CD ROM) and pops up with the "What do you want to do with this
media?" window. However, the drive is empty.
At the same time this happens, I get the following message repeatedly
printed to one of the TTYs:
hda: drive not ready for command

Anybody know what's up here?

Many thanks,
Mark