1995 Dodge Caravan High pitched squeal from rear of car

Our dear old Caravan with lots of other troubles, but still running. Just began making a high pitched squealing noise from near the back of the car. We were told it is the vacuum resonator from the all-wheel drive?

What exactly is this? We are thiking about not having it repaired, is this a safety concern? This is the car that our teenagers drive and we are just trying to keep it going for hopefully 1 more year. However we do not want them driving a car that is unsafe.

Thank you.
Jackie