Nissan Repair: I have a 99 nissan maxima..., nissan maxima, service engine soon light

Question
I have a 99 nissan maxima I just purchased. My service  engine soon light has come on there is also a loud hum sounds like one of the belts. I went to Auto Zone and had them to check the service engine light and the results of that check was a PO400 EGR flow malfunction and a PO325 circuit sensor malfunction. Can you tell me what you think the hum is and the 2 malfunction?

Answer
Keata,

The loud hum is probably a bearing in the alternator or another pulley.  The first code means that the EGR needs to be replaced.  The other code is the knock sensor.  Both are a pain to replace so I would take the car back to where it was bought and see if they will fix them.  Otherwise you are looking at something like $600 to $800 dollars.