"I don't know too much about cars" is the most important thing you wrote here. What this tells me is that you personally are not going to replace parts until your car is all better...you will pay others to do it.
I would suggest you take your car to a Nissan dealer and pay the diagnostic fee to find out what is causing your problem.
My first thought is your CVT is going bad, but I would not expect you to replace the CVT without proper diagnostic testing.
The whine you hear could be the CVT, could be the alternator, could be the A/C compressor, could be the idler pulley, could be wheel bearings, could be CV joints, could be tire noise.
It gets expensive replacing the "could be's"...get a proper diagnosis and go from there.