The ticking noises is the lifters slamming into the valves. They are not receiving the amount of oil they require to lubricate properly. Either the oil level is very low or something else is seriously wrong. Continuing to run the engine like this will lead to very early engine failure.
lifters
The fuel injectors make the ticking noise you hear at startup, especially when the engine is cold (colder temperatures).
Normally loose tappets will cause a ticking sound in the engine. Depending on if you have mechanical or hydraulic tappets you may need to have them replaced or simply adjusted.
The engine
What causes ticking, check engine light, and the check gauges sensor to come on in a 1999 Dodge Durango 5.2L SUV?
Assuming that the engine oil is at a constant pressure, look at the oil sending unit. A bad sending unit or loose wire connected to it can cause an erratic oil reading.
The engine parts are rubbing until the engine oil pressure builds up and the oil starts to lube the parts. Old oil, wrong viscosity, or a clogged filter can cause this to be worse than necessary.
It's a rocker arm tapping at valve stem. Hydraulic lifters (hydraulic rocker mounts) are the common reason for the ticking. If it doesn't go away when the engine heats up, consider replacing the lifter where the ticking comes from.
Possibly just an adjustment on the rockers. Hydraulic system. Hopefully that's it.
On my 1995 Ford Explorer , which has the 4.0 litre EFI , V6 engine , the sending unit for my oil pressure gauge is on the drivers side of the engine below the power steering pump
whoa...OIL pressure or High temp causes the RED engine light to illuminate... Don't keep driving it until you know you've got oil pressure, and it's not overheating...! :)
On a 1991 Ford Explorer , 4.0 litre , OHV , V6 engine : I believe the oil pressure sending unit is on the drivers side of the engine , below the power steering pump