Sporadic clicking noise 4.6 L left valve cover

It reduces Valve train noise and stops oil splatter from exiting engine if cap is left off. I think it just lays on top of valves. Then you install valve cover. I would leave it on

It has developed a clicking engine noise on a cold start. After the car has warmed up, the sound goes away. ... Clicking or a sharp tapping from the valve cover on top of the engine would point to a valve train noise. A dull tapping or slapping sound from the side of the engine block would point more toward piston slap.4 Nov 2011

Cold-start engine clicking is a nuisance, not a disaster - StarTribune.com

check that a valve rocker has not jumped off a valve end and is pressing down on the valve spring retainer.

yes the oil could be getting into the starter housing fix the valve covers replace the starter

Follow the detailed procedure mentioned in the link below to remove replace VALVE cover:----
Click the link below:---
VALVE COVER GASKET REMOVAL GUIDE http://technoanswers.blogspot.in/2012/06/valve-cover-gasket-removal-guide.html

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For more help on these issues,check the link below:---
Car oil leaks from valve cover gasket? http://schematicsdiagram.blogspot.com/2011/12/car-oil-leaks-from-valve-cover-gasket.html

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Lexus RX: Tapping noise under Valve Cover At Low RPM? http://technoanswers.blogspot.in/2012/04/lexus-rx-tapping-noise-under-valve.html
---------- How to replace Timing Belt,Water pump And Valve Guides on Mitsubishi Montero http://repairhelpcenter.blogspot.com/2012/10/how-to-replace-timing-beltwater-pump.html

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2000 Toyota Solara: Valve Cover Gasket Replacing? http://technoanswers.blogspot.in/2012/04/2000-toyota-solara-valve-cover-gasket.html

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Valve Cover Keeps Cracking? http://schematicsdiagram.blogspot.in/2012/04/valve-cover-keeps-cracking.html

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These details will help.
Thanks.

is it just one click noise per push of the pedal or is it a repetitive clicking noise that gets faster as the engine speeds up? if its from the engine, it could be a warped valve making contact with the cylinder head. not a HUGE problem but causes less MPG and less power. to fix that, (assuming you know which valve is warped) youll need a lot of time, a lot of patience, a valve spring compressor (looks like a C clamp,) different socket wrench tools, possibly some screwdrivers, and maybe a couple more misc things. procedure: youd drain the oil, take off the valve cover, detach exhaust manifold from cyl head, remove the cylinder head, use the spring compressor to tighten the valve spring down to remove the old valve, then install the new one, put the head back on, reattach exhaust manifold, put the valve cover back on (might as well replace head and valve cover gaskets while you have the chance) then fill the oil back up. also if you had to remove anything above the valve cover to get to it, reinstall those as well.

overhaul

The clicking noise emanates from the clicking of the
valves, and tappet hammers, under the valve cover.
If these are noisy, it means that it need to be adjusted
for the proper clearances and retightened. Have these
items checked to completely solve your problem. These
valves when properly adjusted will give your car good
mileage.

Check to see if the valve lifters are not making the noise. Turn on the engine and rev it up to about 1500 rpms and see if the clicking is coming from the valve cover area.

There is a vacum powered actuator on the front differential housing on the passenger side. It pushes one way for 2WD and the other way for 4WD. If it gets an erratic vacum signal it can cause the clicking as it goes between 2WD and 4WD. It gets it's vacum from two valves mounted on the firewall just behind the battery(to left). The white line feeds manifold vacum to the valves. Check for vacum at white line with engine running. If no vacum there is a break in line from manifold (not likely in this case). If vacum check the pink and blue lines by applying vacum to each one. The vacum should hold. If not check lines from valves to vacum actuator. If both lines hold vacum check valves. Remove electrical connectors from both valves. Connect a wire from one of the terminals of the valve to ground. Touch a wire from the battery + to the other terminal of the valve. Listen for a clicking sound. If no sound valve is bad. Replace valves(s). Also have someone watch position of actuator shaft as you move the selector between 2WD and 4WD. There should be movement. If there is an intermittent problem sometimes it will and other times it won't.