[enslow]

Use a stethoscope or long stick. Attach one end of the stick to your plugged ear and touch the other end of the stick to various parts of the engine. Begin with the valve covers where the lifters are, then move around to other parts such as the injectors, accessories etc. Be exteremely careful around moving parts.

If you hear the loudest ticking when the stick is attached to the valve cover, it probably is lifters. If you did your LIM and UIM yourself, you'd find doing lifters about as easy, if not easier. I'd probably change valve stem seals at the same time because they're right there.