I posted about this yesterday but I was only wondering what I might be having to replace. Ok, so, it's an 06 k20z1, 85k mi. It's never skipped timing. I've checked compression before and with my leaky tester all the cyclinders showed 170psi (I was only checking for consistency, they're not actually that low) It's always had sort of a valve clattery noise, I hadn't gotten around to adjusting them, it also made a tapping noise that you could hear in the cabin at 2500-4000rpm, and it changed with speed with rpm. I was driving around town, cruising rpm, stop and go traffic, and now I can hear that tapping noise with the engine just above idle, loud. I pulled over and its making a slow steady tap at idle. It all sounds about the speed the valvetrain would move. If I open the throttle body a little bit that's when it sounds like there's a bucket of screws in the valve cover.
Last night, after getting it towed home, I pulled the valve cover off only to find everything is completely normal. Everything is solid, no contaminants, valve tolerances are tight. Turning it over by hand or the starter makes little to no noise, I haven't noticed anything abnormal. I began to suspect the vtc solenoid.
Today, I unplugged the vtc solenoid. I'm going to redescribe the noises here because it's fresh in my mind. The first thing I noticed after start was there was a very loud metallic click (it seemed loudest if i put my stethoscope on the plenum next to the #2 runner) and the loud tap (coming from the intake pulley area) i described earlier. When I unplugged the vtc solenoid, it took about a second, but the metallic click or clatter went away and the tapping dropped in pitch. BUT THE TAP IS STILL THERE! That is what is concerning me... Maybe the solenoid is toast and it's just making noise, I think I'll replace it if somebody does not object.
What in the world could it be?

Edit: Some noises may have gone away or changed because the idle was dropping slowly. I put my stethoscope on the vtc solenoid and that seems to be where the tapping is the loudest.

 

Bump

 

If its gsr or b16 id say lma lost motion theyre little cylinders under the rockers between valve stems they blow out and make sigbificantly annoying noise on these b series

 

Injectors can be quite loud sometimes too. Might be worth listening to them as well. Don't start throwing parts at it until you've properly diagnosed the problem.