When You Car is Okay and When to See a Mechanic
Not every tiny rattle or defect in your car means you should take it to a mechanic as soon as possible, since sometimes cars will have a problem that doesn't necessarily interfere with its safety or stability. That being said, there are times when you want to see an auto mechanic even if your car seems to be running fine, and seemingly minor problems with your vehicle that you don't want to simply dismiss. Note when your car may be okay even if you know something is not quite right, and when you want to see a mechanic as soon as you can.
A car can pull very slightly to one side as a tire gets worn down before the others, or if one tire is slightly deflated. If you notice that your car seems to pull only slightly and you don't need to actually exert extra effort to keep it driving straight, you might check the tread on your tires and the air pressure. If everything seems to be as it should be, you may not have a problem.
However, if your car virtually drives into the curb when you let go of the wheel or you know you need to keep a firm grip on the wheel, it's time to see a mechanic. Your car's tires may be severely misaligned or imbalanced, or the problem could be with the steering column. Don't take chances but have it looked at when the pulling gets severe.
A slight hole in the muffler or other pipe in the exhaust system can cause a rumbling or other unpleasant noise from under the car, and this may not be an issue. However, a louder noise along with rumbling and distinctly worse gas mileage can mean that there is a serious problem with your car's exhaust. Two sections may have come apart or your muffler may have actually come off the exhaust area. This type of problem usually only gets worse with time, and may mean that a pipe or the muffler will eventually fall off completely!
Note too that if your car does have a severe problem with the exhaust system, this can mean not only poor gas mileage but also allowing emission and fumes to get into the cab of the car, as they may not be directed out the exhaust pipe as they should be. Have this severe noise or rumbling checked out as soon as you can.