02 Nissan Altima serpentine belt problem

Have an issue where the belt vibrates about 2" between the alternator and AC. This is a 2.5l with 110,000 miles. It does not occur in park but happens when in drive at idle with the AC turned on. Do not think this happens above idle.
Do you think the belt is loose and slipping causing the vibration?
Maybe the tensioner or AC unit.
Thanks
Steve

Replaced the tensioner and the problem seems to have gone away.

Replaced the tensioner and the problem seems to have gone away.

I once had a similar problem on my 2000 Altima. I ignored the noise for about a year until finally my tensioner/idler pulley completely sheared off due to the inner bearings finally giving way. Unfortunately this happened while I was on my way home on a 6 hour road trip, and I was on the freeway doing about 75 mph when I heard a loud pop inside my engine compartment, followed by a deafening rattle and metal clanging sound. I pulled over and noticed my serpentine belt was shredded and hanging on the remaining pulleys by mere threads. Fortunately I wasn't too far from home but the towing bill was at least a couple hundred bucks. I learned my lesson back then and ever since I have AAA! :)