Im having this same issue. My questions are 1. Are these vales adjustable and 2. Where on gods green earth can I find a Haynes or Chiltons manual for my 97? Even their websites don't have the 3000gt listed. Thanks
valve tappet noise is not a normal thing. The engine is equipped with hydrolic valve lifters that when working properly, remove all valve train clearance and elelveates the ticking noise.
when your hearing the noise, it's not operating as it is designed. Now weather it's a problem or not depends on how much the ticking noise bothers you. it is a sign of wear and or leaking down of oil preasure inside the lifter.
I would at least, check the oil level. for me, the first thing I would do is change the oil. AND if I might add, use the correct viscosity it calls for. Do not thicken the rate. if it calls for 5w-30w then use that. not 10w-40w.
Example, I had a ticking noise on startup in my BMW at 65,000 miles, and used an additive to thicken the oil. It made it worse. I went back to the OEM oil. The ticking has gone away. I currenty have 170,000 miles on the engine and it runs perfectly. If the engine is designed to run a thinner oil, the oil pump flow capasity is greater than in older engines. Running thinner oil is better in the new type engines.
I hope that helps.
BTW; replacing the lifters is probably an expensive repair. Do cheaper things first.