There is an extremely loud, almost metallic sound coming from the rear of the vehicle. After further inspection it doesn't seem to be a heat shield. The rattling only happens every now and again too. When it's having an episode the entire car is affected. The car begins to shake violently and jerks forward. Sometimes the car will shut off completely. The brakes get a bit stiff as well. While I'm accelerating (35-60 mph) everything seems fine but if I fall below or get above that margin all hell breaks loose.
My car has 159000 miles.
My car has an automatic transmission.
You may have a catalytic converter that has broken up inside. The business part of the catalyst is made of ceramic material, (yes just like the clay pots) which is coated with the various precious metals that facilitate the reaction that cleans up the exhaust. If the catalyst is badly overheated, or if you bottomed on a speed bump and it suffered an impact, the material inside can break into smaller pieces. The pieces will sound just like stones rattling around inside a metal can. In the right conditions, one of those stones can shift into a position that blocks the exhaust and you have a sudden loss of engine power. Power that returns as soon as the stone shifts again and unblocks the exhaust. If you can crawl up under the car and strike the exhaust with a soft mallet, you might be able to hear the pieces rolling around. The solution is to replace the catalytic converter. It may also be necessary to replace some other exhaust pieces as sometimes the stones make their way down the system and settle inside the muffler. If you contact Your Mechanic they can send a technician to your home or office to check out your rattling exhaust and let you know if this is your problem and what can be done about it.