Lifter

Do you have one noisy lifter or more than one? These can be caused by low oil pressure, low oil level, sticking lifter, broken valve spring, incorrect oil specification. I would change the oil if it hasn't been changed in a while, make sure you use the correct type as specified for the engine (http://bit.ly/5k7rcr). If that doesn't help check the oil pressure. If it's low, address that, if it's OK, then you have a bad or sticking lifter, or a bad valve spring.