audio files not shown in iTunes

Hi folks,

something is using about 5GByte disk space for 240 audio files on my ipad. iTunes on my Mac doesn't show these files, neither in On my device --> Music, nor in the local data list of other apps. The Music app doesn't show these songs, either. Some other apps *do* show these songs (e.g. CarTunes), but they do not provide an option to delete.

How can I get rid of these unwanted audio files?

Regards

Harri