Squeeking sound on passenger side of car

inside or outside?

Could be something rubbing against the frame.  I saw this problem with 2007 Dodge Caravans where a bolt retainer inside the frame rail was not properly bent over, causing a squeak-creak problem that was very hard to diagnose, but did result in a fix.  It's possible there is a TSB for this problem if the dealership is inclined to look for it.

Probably your right rear leaf springs getting tired. Pretty common from what I've seen, got the same issue myself.

I had a 2000 Blazer that the front end squeeked like a broken bed, i never did find out what it was but i suspected it was the coil springs rubbing on the plates they are mounted in. the rubber goes bad and then stuff starts rubbing. On your xterra it could be the same or something else in the suspension.

I took my 2007 and in on the first oil change and complained of a high pitched noise coming from the front end....passenger side. After 4 times in and them telling me they hear nothing. I got a new strut and strut tower as the metal was rubbing together. Now it is working like a cream puff. I was ready to lemon law the car.