MP3 Player Shufflin' Along

Does anyone know how the shuffle function on car stereos work?  My car 
stereo takes Mp3 CDs.  I have a CD with about 200 MP3s on it.  It's not 
organized in any particular way with files classified in albums or put
into 
folders or anything.  However, the player when it's in Shuffle mode
doesn't 
seem all that random.  

For example, it recently has started about half of the time on Track 77.  
It then generally plays a random song, but within the first 3 or 4 songs 
after that, it will play one of three or four particular songs, which 
aren't related in any way that I can tell, and don't have track numbers 
which are related to each other, as far as I can tell, such as being 
adjacent on the disc, or all ending in 0, or anything like that.

I typically listen to this CD only on short trips, so I'll only play
around 
5-10 songs at a time, so this level of repetition seems unlikely to be the

result of just a quirk of rolling the dice.

Any ideas how it's choosing what songs to play?