Nissan Repair Questions? Ask a Mechanic for Answers ASAP
What year is your xterra, and does it do it when warm or cold let me know ,Thanks ROY!
When the belts are cold they can make noise like a whistle, I would replace the belts and have the idler pulley inspected for noise also. this could be your noise. I have seen a lot of these type of problems when cold, Thanks let me know if you have more questions, ROY!