I wouldn't go as far as to say that they are secret; they just aren't included in the selection of tracks available on the various radio stations. There are a handful of tracks that are only heard in cutscenes and certain locations within the game. It's a weird decision as, if you pay for the license, you think you would want to milk that for all it's worth. However. For whatever reason, Rockstar wanted to be subtle with these inclusions. Here they are below:  • Modern English - I Melt With You • Los Super Seven - Company Gato • Big Country - In the Big Country • Al De Meola - Ritmo De La Noche • Whodini - The Freaks Come Out At Night • Blue Oyster Cult - Burnin' For You