The lifters are adjustable, that's what you do to adjust the valve clearance. If it's only clicking occasionally, it might be something else. Each valve opens every 6.6 seconds at idle.

Still, why not check your valve clearance. Then you won't have to guess & wonder about that.

Not only the valve noise, but the injectors seem to click louder than some other cars too.

 

On the other end of the noise spectrum is the 6-cyl,GL1800 Honda Goldwing motorcycle. That is one quiet engine, and it isn't even under an insulated hood.