driving on country road going about 40 mph is when this “chirping” noise started??? Never this issue before??? Driving in town no chirping so far just started two days ago??? Took to my mechanic he drove it around towns roads up a couple hills came back NO CHIRPING was heard by him??? No idea or suggestion what it could BE???
Could be related to serpentine belt tensioner or any other item the belt drives.
Of course being a Nissan, the transmissions are prone to failure, especially if fluid is not changed every 30,000 miles. Even then failure rate is high.
When my truck chirps like that, the problem is usually the rear driveshaft u-joints need to be lubed. Suggest to do some experiments to decide if problem only occurs in certain gears, when coasting in neutral, etc. Sometimes I can tell what part of the truck the chirping is coming from b/c I hear it loudest when aligned with & reflected off a traffic-wall or nearby car.
the only other chirp sounds I’ve heard from my cars is a loose accessory belt. But that is usually loudest when engine is first cold-started, and can hear it best at idle and lower speeds.
Just a thought …If the country roads are a lot bumpier than the roads in town, it could be in the suspension. try pushing up and down on each corner of the vehicle and see if you hear the noise.