Restarting the Windows Management Instrumentation Service "solved" the high CPU problem for me.
But as a consequence Garmin Express did not find my watch any more. Did not see the link between GE and WMI until I read this...
Thanks for the hints... Will try to find a workaround for this. Restarting WMI service to get CPU usage down and rebooting to get GE working again is not a solution ;-)