My wife's Mazda Millenia did this same thing at 34,000 miles, the engine had a stuck lifter. I drained some oil out, added a quart of engine flush and ran it about ten minutes, did an oil change and added some Marvel's Mystery Oil, and ran it for a few hundred miles. I changed the oil again, and the noise seems to have gone away.

Too many 4x4's, not enough time or money