Used space doesn't add up

I’ve had a 4 GB unit for a couple of years and loved it.  Just purchased an 8 GB one and having an issue.  When I add up the file space on what I’ve loaded it adds up to just about 4.5 GB used.  But the unit is showing that I have used 6.57 GB out of 7.35 (I understand where the other .65 went so that is not my problem)  I have tried removing all of the audio books (which adds up to just about .5 GB) and it reduced it almost exactly so I put them back.  I don’t really want to remove the music as it took quite a while to put it on in the first place.

Thanks in advance.

Donna

That is exactly what I decided to do after posing my message earlier today.  Whatever confusion my new Sansa was having was cleared up once I reformatted.  Thanks for the info.