2.5L 1998 ranger. Tapping/Clacking noise under light throttle, coasting at 50mph, or when I let off throttle under load it will clack on the Rev down for about 1-2secs. Sounds like a collapsed lifter, but I pulled cover and verified that rocker arms and valve clearances were all tight. No mushroomed ends, loose rocker arms, or uneven wear. Checked hydraulic lifters and all seem to be strong and clean. I cannot for life of me figure this out. Been years already lol. Not getting worse, not any better. Makes most clack when in park and revved up to about 2000-2500rpm and held there. It is also not timing belt slap or anything up front (just did fb, tensioner, wp). Even tried checking with a steth and still cannot pinpoint it. Thought maybe could be piston slap but that's more of a knock than a tap/clack. Any ideas?
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I just pulled the cover and checked rockers and valves. Nothing is loose, or mushroomed. Changed listers anyway, added shims under lifters also. Still clacking. Seems to be getting worse after 7-8yrs of no change. Now it's doing it under any sort of load while driving. I'm staring to wonder if it's the beginning of a rod knock, but didn't think a bearing would go 7-8yrs without any change prior.