Check owners manual. If the rear end has not been opened up or worked on, check the level by removing the fill plug. Your vehicles are not really that old, but if you feel compulsive, you can certainly drain and change the diff lube. This is there to keep all the gears, bearings bushings happy and slick.. Not sure, but between 30,000 and 50,000 miles is an OK interval. But, again check your owners manual for specifics..
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.