Oh, I had the unannounced audit this year too, just 3 weeks ago! Yes, you should contact your CB and ask to send you the Unannounced Audit Confirmation letter and Audit Questionnaire. (at least, that's what I got from SGS) Below is the information you should provide your CB prior to the audit - it's an excerpt from the questionnaire I've received:
INFORMATION TO BE PROVIDED BEFORE THE AUDIT
Shift Pattern/normal working days/nights:
Sat:
Sun:
Mon:
Tue:
Wed:
Thu:
Fri:
Block out dates (Maximum 15)
Planned Shut Downs (these are not considered to be block out days)
Location for auditor to report to (e.g. security/reception).
Site contact for the auditor to request
ANY SPECIFIC SITE INSTRUCTIONS / HEALTH AND SAFETY REQUIREMENTS