Car producing a ticking sound upon start up?

There are a number of reasons owing to this:

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  engine piston

  Damaged reciprocating components of the engine such as pushrods, valves and pistons. If these are worn out or damaged in kind of manner and are not replaced the sound may migrate from ticking to whining or clunk, evidently showing more signs of damage.
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  oil pressure light indication on dashboard

  Not enough lubrication on components. If there is a low amount of oil in the system, this may cause a ticking noise from components in the valve train. Low oil is usually accompanied by overheating and damage on the seals and gaskets. If these happen concurrently, then you'll know what to suspect primely.
• Valves not properly set or adjusted. The pushrod which controls the rocker arm from the camshaft needs to be at precise distance from the valve, and if not, it will cause a ticking noise from the rocker assembly
• Warn out bearings. Bearings hold components to a reasonably fixed position. If a bearing warns out and loosens, the corresponding rods will move unnecessarily and thus causing a ticking noise.
• Injectors firing. This you'll need to worry about less because injectors will always need to open and close to allow in and out passage of fuel. Under high pressure and a well functioning pump, a ticking sound will be heard unless if it appears too absurd