Ford Repair: Nosie Tappets, mobil 1 oil filter, ptfe teflon

Question
I have a 98 ford f-150 4.6 ltr engine. Has 86,000 miles
The tappets have been becoming noise, at idle and seems to disappear when I riv or run high Idle.
What should I do to resolve the problem?
I started to here noise a few months ago.
Do I need to start using a heavy wt oil or add STP additive?

Answer
I only recommend using heavier oil if their is a leak. I tell you what. Go to Wal-Mart, of all places. In their automotive section is an oil additive made by greased lightning of all things. Greased Lightning has PTFE, Teflon. I have seen this stuff do miracles on engine noise. Myself, I prefer Mobil 1 Synthetic, with the Mobil 1 oil filter. Their oil filter has filtration comparable to hepa filtration in a vacuum cleaner. When you pull off an old Mobil 1 oil filter it is unreal how much it weighs. Have you ever ran the truck low on oil or went way too far between service intervals? Have you had the timing chain serviced yet?