Outlook 2003 commands hang

I am running Outlook 2003 with XP Prof SP3.

In Outlook mail, commands hang for several minutes before completing with egg timer showing, then starts again as soon as the next command is clicked. After a while this clears and works ok, but then suddenly begins again for no reason.
The same happens in Contacts, so there seems to be some process running in the background.
I ran scanpst which improved things for a short while, but each time it comes back again.

Help to resolve this please.

rgds
Bar457