[JustSayGo]

Your first step should be to find out what codes are stored in the computer now. AutoZone will read the codes and tell you what they are with out charging you. Your 2000 Altima probably needed a tune-up if the sparkplugs have never been replaced. Are you saying that the tune-up eliminated a slight hesitation? There may be a loose connection inside of your radio causing intermitent function. It is very unlikely that there is any common cause with the SES light indicating that a code has been stored in the ECM and your radio. If the dealer charged you to eliminate or diagnose the cause of the codes stored in the ECM, and you still have the same codes, they owe you for something. If you have a code related to the MAFS, the other shop owes you. Your repair invoices should list the codes. Too much water? Must be some kind of miss-understanding.