RME multiface/cardbus problem

Whenever I start or stop playback in the middle of audio, I get a loud click/glitch before playback commences/stops.

I have a centrino laptop (2Ghz, 1Gb RAM), with a RME cardbus interface to a Multiface. I'm running Sonar 4PE on XP.

This is with 44.1kHz, 16 bit audio, and occurs with a single stereo track of audio and no plugins.

I don't think it is a latency issue - I can set the value very high and it does not prevent it. I have the clocking of the multiface set to internal, and I'm not connecting any other digital devices to it, so I don't think it's a clocking issue.

Anyone got any ideas?

Cheers,
Kai