That annoying tapping sound you hear at idle is not your lifters, injectors or your headers. There is an emission control component called the PWM-vacuum switching valve screwed to the intake manifold on the drivers side. You can access it by removing the plastic shield over the intake manifold. It is held in place by a single screw. This thing activates when the vehicle is at idle and at temperature.
To minimize the tapping sound coming from it, you nee to isolate this component from the manifold. The manifold is resonating the sound from the valve making it loud.
Here's what I did to minimize the noise:
You will need 2 rubber o-rings ( I used R03 nitrile o-rings) and a 10 mm Nutdriver or wrench.
After removing engine cover,
remove bolt that holds the valve to the manifold (no need to disconnect any lines or harness)
Place an O-ring on the bolt and push it to the head of the bolt.
Slip the bolt through the valve and slide the other o-ring over the bolt.
re attach valve tightening enough to compress the o-ring and snug the bolt. The o-rings should be enough to keep the bolt from vibrating out.
Replace cover and enjoy the silence!
***This may not eliminate this noise, but it sure quieted mine down.
So, don't worry about trying different weight oil (use the recommended only) or any other drastic measures. From what I have read, most if not all toyotas in the last 5 years have this tick. Maybe the factory should do something about it. I think that Toyota should find a quieter valve or make an isolated mounting kit.