I can't help with the mechanical aspects of your question but maybe can help with the warranty aspects. Since you live in a major metropolitan area, there must be loads of good and trustworthy mechanics. Cartalk lists mechanics that their readers/listeners have had that they would go back to here:
Car Talk
Once you get an answer to your question from a mechanic that you believe knows what they're talking about, have them do a work order and take it back to your dealer. I agree that if you first raised these issues while under warranty the dealer has an obligation to address the problem on their dime. If they don't, in my experience Nissan has a very effective procedure for addressing greivances laid out in the manual. I used it once and was very satisfied. I also have an 02.