I own a 93 2wd pickup with 128000 miles on it. When i purchased the truck it had only 35000 on it. I religiously change the oil and filter at 3000 miles. i have had no trouble from the truck until now. at around 70000 miles i noticed that the valve cover gasket was leaking, and i needed new belts and hoses, so i took it to a local shop to have the belts and hoses replaced and to have a new valve cover gasket installed. since they were gonna have the valve cover off i asked them to adjust the valves.(big mistake) i thought that the valve adjustment might help bring back some lost power, however when i got the truck back i couldn't tell the difference. at around 80000 miles i noticed a sound comming from the valve cover. it sounded like a BB was bouncing around in the valve cover!! it didn't really sound like the valves or a valve was tapping it sounds cravy and it does it intermittently. but thats not the sound that im worried about. a few days after i changed the oil at 127000 miles i heard a loud tapping comming from the valve cover. sthis sound is deffinetly a valve or lifter. so i checked the oil to and it was full. this is turning into a long post! i don't want to leave anything out. i forgot to say that at about 100000 miles i switched oil. i went from bulk 10w30 to havoline 30w.
im gonna stop typing now because my fingers hurt!

id check the timing chain. Around 130,000 mi the guides on the chain let loose and lets the chain wear a hole through the block. That sound may be the plastic guide that fell off bouncing around in there and / or chain hitting the block.

-Adam-

Just bought a 93 tota with a 22re. I had a valve cover leak and found the nuts loose on the cover. After tightening I had a tapping noise. By loosening the front left nut the noise went away. I assume the gasket is old and squashed to far. Just thought I'd give you some heads up info.