Lot of times if it's a low level ticking sound, it could be an exhaust leak.
Does the "low oil pressure" light ever come on? Make sure the oil level on the dip stick is at the full mark. If it's a loud metallic sound, then you may possibly have low oil pressure which could be caused by several factors; worn rod/main bearings, plugged up oil filter, dirty oil pickup. Most of the time it's the oil pump which may be worn and not producing the proper oil pressure/volume. This could cause the chain tensioner to lose tension on the timing chain thus creating the noise.
You can check the pressure very easily by installing a temporary mechanical oil pressure gauge. You would remove the oil sensor which is located next to the oil filter and install the mechanical oil pressure gauge in it's place; you may need to get an 1/8 BSPT to 1/8 NPT adapter to hook up the gauge.
With the engine fully warmed up, the pressure should be as follows:
idle - at least 14 psi
2000 RPM - 43 psi
