A common failure of an exhaust pipe is that it rusts in two near the muffler, making the exhaust very loud - loud enough to get you a ticket.
There's no reason for this to happen: Periodic inspection will catch the problem in time so you can deal with it before it gets out of hand. But what if it does happen to you, maybe when all the garages are closed, or when you can't afford to replace the exhaust system for a while - what do you do?
There's an inexpensive emergency repair you can make that, done properly, will make the system quiet again, maybe even as quiet as when it was new. The only caution is that this is strictly an emergency repair, and temporary; it should not be relied on for any great length of time.
First raise the car so you can get under it. Use jack stands or sturdy metal ramps - don't rely on the bumper jack.
Open a tin can at both ends and, with a pair of diagonal cutting shears, a hack saw or an old pair of scissors, cut the can from top to bottom.
You'll also need some wire, some aluminium foil and two screw-type clamps, the kind you can get at gas stations, hardware stores and auto-parts stores, in many sizes. You want clamps a little bigger than the diameter of the exhaust pipe.
Unscrew each clamp until you can pull it apart. Now crawl under the car with your prepared tin can, your two clamps and a screwdriver.
Pull the two pieces of the exhaust pipe together and wrap the tin can around them, watching out for the sharp edges. Put a clamp on each end of the can and screw it as tight as you can. This will hold the exhaust pipe together.
The exhaust pipe will probably try to pull back apart as you try to tighten the two clamps. If this happens, tighten one clamp first, then slide the other piece of pipe in and tighten the other clamp. The two clamps will hold the broken exhaust pipe secure.
Next put the aluminum foil around the can, sealing off, as much as possible, all openings that will let exhaust gases, and therefore noise, escape. Don't be stingy with the foil. Wrap a few turns around the repair, then wrap wire tightly around the foil to hold it in place. Wrap some more foil around the repair, wire it in place, and so on - until you have a considerable thickness of foil completely covering the repair.
Even better, after you've put on the first layer of foil, is to wrap on a layer of exhaust system repair tape, which adds some thickness to the repair, helping reduce noise. Then layer on more aluminum foil.
Now your car should be considerably quieter, maybe even as quiet as before.
As soon as possible, either replace the exhaust system or have it replaced. It's also a good idea to drive with a couple of windows open a little, to help, ventilate the car in case deadly exhaust fumes are getting inside.