I like to routinely check documents against backups by comparing MD5 
signatures. 

However, I find this impossible with Excel files because the MD5 value 
changes just from opening and closing documents.

I have tried this with a blank document on both Excel 2003 and 2007.

I do not have this problem with Word documents or any other type of file. 

Could someone please advise if there is an Excel setting that is causing this?