Tapping is more than likely a deqd or stickng lifter.
I will share a old school trick that was used long before any cleaning chemicals was avalible.
Trans fluid, get yourself a shotglass, have engine fully warmed up.
Pour one shot of trans fluid into oil fill, let idle for 15 mins.
If it doesnt go away or start to change volume, pour in second shot.
Listen carefully for changes! By se ond 15 min idle if. Noise doesnt go away, let it sit over night.
Fire it up and let warm up. Noise should be gone completly.
If not its dead lifter, bent pushrod or rod knock.
Regaurdless, change oil.
To check for bent push rod. Pull one at a time, clean it with steel wool then roll it on glass, if it wobbles. Replace it. Also that lifter is suspicious.
Write anything you fi. Down and check them all.
You can start on your low compression cylinder, as its suspicious alrdy.
Btw, after running the trans fluid, recheck compression. You may find its higher than the initial 150, as comperssii. Rings do stick due to carbon fouling.
Pouring a shot of trans fluid directly into that cyclnders spark plug hole, and lettng soak over night is best method of freeing stuck rings.
then while plug is out and coil unpluged, crank motor over untill no more trans fluid sprays out of plug hole.
You will want to change oil after these methods as trans fluid is a bigtime detergant and will eat up all oil sludge, carbon etc. But will ruin the oil.
Back in tye day we would pour in almost a quart of tranny fluid to clean out severly gunked up engines, even would pou it down the carb throat to clean valves.
Just now days with everyone going green and a million types of cleaners. The old but best methods are forgotten.
GL on tracking that noise down.
---------- Post added at 02:06 PM ---------- Previous post was at 02:05 PM ----------
Btw, i typed all that on my iphone.