Is your car making a rattling noise when you drive it, or maybe even when it's idling? Something is definitely wrong, and there are a few different problems that might be causing the noise. Here are some of the top possibilities.
A Broken Timing Belt
The timing belt is a component that makes sure the various cylinders in the car's engine open and close at the appropriate times. If this belt becomes worn or frayed, it may cause your car to rattle. As the problem becomes worse and the belt becomes weaker or more worn, you'll have bigger problems -- such as the engine misfiring or refusing to turnover when you go to start the car. Replacing a damaged timing belt is a pretty straightforward repair that most any auto repair company should be able to complete.
A Cracked Catalytic Converter
The catalytic converter is a component of your car's exhaust system. It can crack, which causes a rattling noise that is usually most obvious when the car is idling and when you pick up speed. Though your car may run just fine with a broken catalytic converter, it will probably not pass emissions testing, so you'll need to have this component replaced before your car is due for inspection. Replacing a catalytic converter can be a bit costly, so get a few estimates before hiring an auto repair service for this one.
If your car has been leaking oil, there may not be enough oil to fully lubricate the car's engine. This can cause it to rattle back and forth. If your car's oil light is on, this is probably the problem. Have your mechanic look for leaks in the oil lines and oil tanks. Some leaks are easier to repair than others, but you do need to have this problem fixed since running a car with low oil levels can cause it to overheat and burn out the engine.
If your car has a lot of miles on the engine, the pistons may be worn down to the point that they do not slide into the cylinders properly. The problem causes some rattling, which us usually most noticeable before the car warms up completely. If this problem is rather minor, you may not need to have anything done about it. If you really care about the car, you can have the engine overhauled to resize the pistons.