2012 Nissan Rougue whine noise acceleration

My buddy just bought a used 2012 Nissan Rogue S AWD with 37,000 miles. We have had a couple of nice days so we notice with the windows down there is a whining noise when accelerating on a hill then goes away once up to speed or when accelerating on level. It sounds like the CVT or transfer case but not sure. It’s noticeable that my buddy who knows nothing about cars brought it to my attention. The CVT fluid looks clean and full with no burn smell. There are no trouble codes and it seams to drive and run just fine. I just fear something maybe going wrong with the CVT after all the horror stories I’ve read about the going bad and started failing with a whine noise. I haven’t checked the transfer case fluid condition yet.