Go to your local parts place and spend less than $10.00 on a mechanic's stethescope (sp?). A piece of hose as posted above can be used, as can a screwdriver (blade on engine, ear to handle), but if you're not a regular shade-tree mechanic, the right diagnostic tool will quickly tell you which part of the engine is ticking.
I suspect one of your hydraulic lifters is the culprit. You need only replace the faulty one(s). Try a good can of top end cleaner first, in case the problem is just a bit of blockage in the lifter oil intake bore.
An individual lifter can be checked by pushing down on it with a hammer handle and feeling the resistance. Compare with the ones nearby the suspect one and the collapsed lifter will take little or no effort to push the end down (no hydraulic pressure from oil inside).
Examine the cam lobes in the area where the ticking is coming from. Often, the lack of pressure from a bad lifter will allow the rocker arm to dig into the cam lobe and score it. If not too deep, past the case hardening, a new lifter/rocker will get you many more miles of quite engine life.

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1986 560SL
2002 Toyota Camry
1993 Lexus