Starting your car and hearing ticking or tapping sounds from under the hood can be quite unnerving. Problems that can cause such noises range from relatively minor to extremely severe. By listening you can often determine the source of the noise and figure out whether it's something you can take care of, you will need a mechanic for or if it's time to shop for a new car.
To determine that the sound is actually coming from the engine press on the throttle pedal. Noises that vary with engine speed will be coming from the engine. If the noise varies with vehicle speed, no matter the engine speed as you shift through gears, are coming from somewhere else. In the rare case you hear a noise that doesn't vary in speed it will be completely unrelated to the engine or drive train.
Ticking when started cold
If you hear a relatively high pitched or soft ticking coming from the upper part of the engine when you first start your car that goes away shortly after starting you probably have little to worry about. This is especially true if it primarily happens in colder weather.
The valves that allow the fuel and air mixture into the engine and the exhaust out are usually operated by hydraulic lifters. These lifters require a certain oil pressure to operate properly. When the car has set for a while the oil drains out of the engine into the oil pan. Until the oil pump builds enough pressure these hydraulic lifters there will be a slight ticking noise. In colder weather it often takes a bit longer for the oil pressure to build making these noises more common.
If you do hear such a noise that goes away you should check the oil level to make sure it isn't low. If you do have a low oil level topping off the oil might help to reduce the incidence of this noise. If the oil level is good it is probably nothing to worry about.
Ticking that doesn't go away
If you have lifter noise that doesn't go away when the engine warms up you might have a more serious problem. This could be a sign that the oil level is too low to build adequate pressure to allow the lifters to operate properly. Check the oil level and fill if necessary.
If the oil level is adequate and the noise continues the problem is more serious. This could indicate blocked oil passages, failing lifters or a failing oil pump. An experienced mechanic can perform further troubleshooting to better identify these issues.
Louder tapping noise
If you experience a louder tapping noise from the lower part of the engine you likely have a very serious problem. In the most severe cases it can sound like your vehicle is coming apart. These noises are associated with the bearings on the connecting rods or a broken connecting rod. Whenever you hear such a noise you should stop your engine as soon as you can do so safely and have your vehicle towed to a repair facility. It is likely that, once you get an estimate for this repair, you will be considering the purchase of a new vehicle.
Loud tapping noises from the bottom of the engine indicate failed connecting rod bearings, failed crankshaft bearings or a broken connecting rod. To repair these problems your engine will have to be removed and the bottom end of the engine will need to be disassembled and rebuilt. In really sever cases a broken connecting rod can cause so much damage inside the engine block that the entire engine will need to be replaced.
Hopefully the noises coming from your engine will be minor and this will help reassure you about the condition of your vehicle. If not, at least the knowledge of where the real problem is may help to protect you from an unscrupulous mechanic.