I had this problem in my 92 Plymouth Voyager. You need to replace the tension pulley. They get old and become out of alignment.
One of the pulleys is out of alignment,usually it is the tension pully. Replace it and problem will go away.
You cannot adjust the belt tension on a 2000 dodge grand caravan. This vehicle is equipped with an automatic tensioner. If tensioner is frozen or will not hold the belt tight, it must be replaced.
You can do that by replacing the tensioner
drive belts tensioner/under chassis
A proper alignment shop can do it, it takes special equipment.
The belt tensioner is self-adjusting.
its on the left side. its the easyest pully to see.
When I took my 96 Caravan to be aligned they said there is no rear adjustment that can be done.
Pull on the belt and you can see how the tensioner moves. Put a wrench on the bolt.
I cant answer that because alternator tensioner fell off and I'm having trouble finding one.
They are not adjustable. They are self adjusting, if it is not adjusting properly it probably needs to be replaced.
Check all of the pulleys to make sure they are running in a straight line.