Engine was rebuilt in 2016...getting a tapping sound when warmed up...no check engine lights...I've experienced broken valve springs & spun bearings...I only hear the tapping when warmed up...no check engine lights...doesn't seem to be any loss of power....could it be valvetrain related? Rocker arm or lifter?

Most engines now use hydraulic lifters and they can leak a little, this causes space between then lifter and the push rod. This results in a tapping noise that goes away when they get warm or fill back up.

Pinging or combustion-related knock could be caused by a partially clogged fuel injector, low fuel pressure at the injector, or hot carbon deposits in the cylinder triggering premature ignition. Mechanical knock could be a worn or broken rod bearing, or (more rarely) a worn crank bearing. A worn or sticky valve tappet or lifter often makes a tapping sound, particularly if the oil pressure is low.

If your Check Engine light is on, get a readout of the error code; it may help you narrow down the cause. An experienced mechanic may be able to tell you more just by listening to the sound,

Check this information about "engine noses"...

A clicking or tapping noise that gets louder when you rev the engine is probably "tappet" or upper valvetrain noise caused by one of several things: low oil pressure, excessive valve lash, or worn or damaged parts.

First, check the engine dipstick to see if the oil level is low. If low, add oil to bring it back up to the full mark. Is the engine still noisy? Check your oil pressure. A low gauge reading (or oil warning light) would indicate a serious internal engine problem that is preventing normal oil pressure from reaching the upper valvetrain components. The cause might be a worn or damaged oil pump, a clogged oil pump pickup screen or a plugged up oil filter. Using too thick a viscosity of motor oil during cold weather can also slow down the flow of oil to the upper valvetrain, causing noise and wear.

COLLAPSED LIFTER NOISE
Worn, leaky or dirty lifters can also cause valvetrain noise. If oil delivery is restricted to the lifters (plugged oil galley or low oil pressure), the lifters won't "pump up" to take up the normal slack in the valvetrain. A "collapsed" lifter will then allow excessive valve lash and noise.

VALVE LASH NOISE
If you can rule out lubrication-related problems as a cause, the next step would be to remove the valve cover(s) and check valve lash. On older import engines, mechanical lifters require periodic valve lash adjustments (typically every 30,000 miles). Too much space between the tips of the rocker arms and valve stems can make the valvetrain noisy -- and possibly cause accelerated wear of both parts.

To measure (and adjust) valve lash, you need a feeler gauge. The gauge is slid between the tip of the valve stem and rocker arm (or the cam follower or the cam itself on overhead cam engines) when the piston is at top dead center (valve fully closed). Refer to a manual for the specified lash and adjustment procedure. Also, note whether the lash spec is for a hot or cold engine (this makes a big difference!).

On engines with hydraulic lifters, oil pressure pumps up the lifters when the engine is running to maintain zero lash in the valvetrain. This results in quiet operation. So if the rocker arms are clattering, it tells you something is amiss (bad lifter or worn or damaged parts) or the rocker arms need adjusting.

DAMAGED ENGINE PARTS NOISE
Inspect the valvetrain components. Excessive wear on the ends of the rocker arms, cam followers (overhead cam engines) and/or valve stems can open up the valve lash and cause noise. So too can a bent pushrod or a broken valve spring.

RAPPING OR DEEP KNOCKING ENGINE SOUND
Usually bad news. A deep rapping noise from the engine is usually "rod knock," a condition brought on by extreme bearing wear or damage. If the rod bearings are worn or loose enough to make a dull, hammering noise, you're driving on borrowed time. Sooner or later one of the bearings will fail, and when it does one of two things will happen: the bearing will seize and lock up the engine, or it will attempt to seize and break a rod. Either way your engine will suffer major damage and have to be rebuilt or replaced.

Bearing noise is not unusual in high mileage engines as well as those that have been neglected and have not had the oil and filter changed regularly. It can also be caused by low oil pressure, using too light a viscosity oil, oil breakdown, dirty oil or dirt in the crankcase, excessive blowby from worn rings and/or cylinders (gasoline dilutes and thins the oil), incorrect engine assembly (bearings too loose), loose or broken connecting rod bolts, or abusive driving.

Bearing wear can be checked by dropping the oil pan and inspecting the rod and main bearings. If the bearings are badly worn, damaged or loose, replacing the bearings may buy you some time. But if the bearings are badly worn or damaged, the crankshaft will probably have to be resurfaced - which means a complete engine overhaul or replacing the engine is the vehicle is worth the expense.

ENGINE PINGS OR KNOCKS WHEN ACCELERATING
The cause here may be Spark Knock (Detonation) caused by an inoperative EGR valve, overadvanced ignition timing, engine overheating, carbon buildup in the combustion chambers, or low octane fuel.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day

What engine? I've never encountered a broken valve spring on a 3.3 or 3.8 liter. Broken rocker arm shaft mounts are a known issue on the 3.3 liter.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

A rhythmic metal on metal noise in an engine usually follows a classic rule: valves tap and pistons knock. If the noise is rhythmic with the speed of the engine and incrementally increases when the engine speeds up, then it is one of these two issues. All you need to answer in this case is whether your noise is a tap or a knock. On the other hand, if the clanging sounds more like an old diesel engine and increases in volume when the engine accelerates, then the problem is pre-ignition. If the problem is simply pre-ignition, then you will need to check your ignition system, including the knock sensor, crank sensor, and all your spark plugs and coils. This is the simplest thing to do first. Unplug each coil one at a time to verify that the engine loses power for each one. Valve tap can be caused by lifters or a broken valve spring. To diagnose this, you need to remove the valve cover and check the lifters. Are any loose when you try to move them up and down by hand? Engine knock signals that your engine needs to be rebuilt with new piston rods and bearings. It is not a good idea to drive very long with either condition or you could end up causing more damage and get stuck on the side of the road.

posably could be a miss alignment or bent valve could be a lot of stuff check the compression this should tell you

that is odd,thinking possibly a burnt valve tho,check compression yet?

Spun bearing = time for engine rebuilt. Sounds like your engine spun a crank shaft bearing or connecting rod pin is loose or worn out. If your lucky, it may just be a worn distributor gear that is causing your knocking due to bad timing.
Good luck and try not to run the engine with the knocking, it may be a simple fix that will lead to a major problem.
Thank you for using fixya and is the engine oil level right where it suppose to be???

the cure depends upon the problem: Knocking is usually down low and is generally an engine bearing problem. If you hear a tapping noise (lighter than a knock) and oil pressure is good it can be caused by wear of the pivot for a rocker arm, a worn lifter or lifter and camshaft or a broken valve spring. Tapping can also be caused by low oil pressure in which case it can be due to low oil level, obstructed pump pickup or worn engine bearings. If you are unfamiliar with any engine repair, get a chilton or haynes manual to guide you through whatever needs doing.

You might have a bad hydraulic valve lifter (assuming this engine has them)... you could try an aftermarket product designed to unstick valve lifters.... any auto parts store carries them.