Q:

Where are all those audio files on the iPhone? 

My 8GB iPhone 3GS claims, in iTunes, that it contains 3 GB of audio files. 
However, in "Music" only 1 GB of files show up, in "Podcasts" are another 72.8 MB and there is nothing in "Books" and "Movies". 
Where are the remaining 2 GB of audio files? 
Edit: I also notice that there are podcasts in one of my playlists that are not in the "Podcasts" category (or the "Music" category).  Whey are they stored?  In fact only two podcast episodes are in the "Podcasts" folder but about 10 are in the playlist. 
I upgraded from iOS 4.3 to iOS 5.1 yesterday.  In the process the phone was backed up and restored a few times.  Might that have something to do with it? 

A:

In the process the phone was backed up and restored a few times.  

“A few times”?  That doesn’t sound very good…
Try resetting your iPhone to factory conditions and restore your backup once.  Make sure the backup doesn’t get interrupted — it should be able to finish in one sitting!