If your exhaust system is coming loose, it is possible that the brackets and bolts which hold the exhaust in place on the undercarriage of the car, have either come loose, been broken from road and vibration stress, or maybe a bolt fell off.   Often, this is just the beginning of the problem; and it is the perfect time to have a repair shop put the car up on a hoist to see what is happening.  If you have the brackets tightened or replaced now, when you have just noticed a problem, the cost for the repairs, and parts is minimal.  If you wait, and continue to drive the car, eventually part or all of the exhaust system will fall down and be dragged along the road until it breaks off.  By that time, you will really have an expensive problem.  Get it checked out as quickly as you can.  The catalytic converter, and the exhaust system itself can be costly to repair or replace.