Metal tapping noise at idol. it goes away as soon as you give it gas,the car runs great. i need help finding the noise.

My 1996 Mazda MPV V6 has had a tapping noise problem ( under the valve covers) for about 3 years and I have tried many oil additives and different oil grades with no resolution. Last week I tried the lightest synthetic oil I could find, Mobile 1 5W-20. As soon as I started the engine it had no noise at all. I have started it many times since and still no noise. I assume that the oil passages have become narrow over the years ( or are narrow by design) and this light oil is able to move through them quicker and keep the hydraulic lifters under proper pressure. You may have to beg or threaten your mechanic to use this oil. He will try to scare you into using a heavier oil. He may just be ignorant. But, stand your ground, say Mobile 1 synthetic 5W-20 or I will go elsewhere.

The tapping is most likely your lifters, These makes the noise when oil is broke down or low, Maybe even a weak oil oump, Usually it is still making the niose on accl. and covers up by engine noise. Good luck to ya.