Infiniti I30 Starter Noise

THis weekend i went to start my 2000 I30, and I heard this awful screeching noise. Thought it might be the belts, but it was not. The sound was coming from the driver side of the hood. The service engine light is also on. But I have seen this appear and disappear throughout the weekend. I am not sure if this could be the alternator or not?
Has anyone else experienced a similar problem? If you have replaced the alternator, how much did it cost?
Does anyone know where i can find a list of codes that a dealer would use to diagnosis problems with the I-30?

Any help recieved will be greatly appreciated.

Thank you,
'Zo