I'm afraid you are mistaken about the metadata issue - all wav files contain metadata, as it's a part of the file specification. And it won't necessarily be the same from one version to another. Opening a file created in a later version and then resaved in an earlier one will replace that metadata set with the data from the older version. If you open the metadata tab and click on the three dashes and select 'metadata display' you can expose all of the fields. Just a difference in the creator tool data (which there will be) could account for a 5k difference - that's not very much!