Should your vehicle's engine run low on engine oil it could cause it to make a loud "ticking or tapping" noise. This noise is caused by an insufficient amount oil being pumped into the top part of the engine. A simple check of the engine oil level will help you determine if the system is low.
It's not unusual for the engine to make a tick or tapping noise when first started cold. When the car has set for a while, the oil drains out of the engine and down into the oil pan. Once the engine is started, the oil pump circulates the oil throughout the engine allowing it to build pressure. Until the proper oil pressure is achieve you may hear this slight ticking noise.
In colder weather it often takes a bit longer for the oil pressure to build making these noises more common. If the noise remains after the vehicle has come to its normal operating temperature, have a professional inspect the engine to determine the cause of the noise.