So you're hearing a sharp tick tick tick under the hood? First things first, be sure your cat didn't steal your Rolex to hide out under the hood with a few buddies. If you're sure this isn't the case, read on and let's see what we can figure out.
A few questions:

• Is the sound definitely coming from under the hood, in front of you?
• Does it tick more in the morning, and seem to go away when you start driving? Or does it tick all the time?

If you answered yes to the first question (it's coming from under the hood) and it ticks all the time, the first thing to do is check your oil level. If your oil is low, it can cause the engine to tick because not enough oil is making it all the way to the top. If it only ticks a little when you start up in the morning, don't sweat it. It takes a sec for the oil to circulate through the entire engine after it drained to the bottom overnight. If the tick doesn't go away, or seems to have been getting louder and louder over time, you should take it to your mechanic to check your valves. However, if you keep your oil level where it should be, and the ticking doesn't bother you, there is very little chance of anything catastrophic happening. Just turn the radio up!