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Many possible causes....Too little info to make an intelligent suggestion. Try charging the problem vehicle's battery with jumper cables for 2 minutes with the supply vehicle running at fast idle (or about 1500-2000 RPM, if it is tachometer equipped) before you try to crank the problem vehicle on a cold morning. If it starts right up, you likely have a weak battery that needs replacing.
Hard to say over the internet but I will try to explain. If the noise is a distict KNOCK KNOCK and it sounds like it is coming from the bottom of the engine, then it most likely is a rod or main bearing. If it is a TAP TAP noise that sounds like it's coming from the top of the engine, then most likely a valve lifer is failing/failed.
the fact that it goes away when the car is warm, makes me lean towards a bad lifter. Normaly if a bearing is bad and knocking, the noise doesn't go away.
The KNOCK noise will be somewhat hollow sounding and the TAP TAP sound will be more solid. If the KNOCK KNOCK is solid, then a rod or main bearing has most likely failed to the point that a new/reman engine will be needed.
might be the valves have been damaged running without oil
- or the crankshaft / camshaft / main bearings
most probably you have to let the engine be rebuilt by a mechanic
(expect cost of more than US$ 2.000)
or get another (used) engine at a scrapyard
If it is a 'squealing' noise it's probably the alternator/power steering drive belt. Before you turn on the engine in the morning, lightlt smear or spray some oil on the inside of the drive belt to lubricate it. If the squealing stops/disappears, then that's the fault ..
That squealing noise can be caused by an incorrectly tensioned belt, or a worn belt. Replacement is the only option.
The other frightening sounds can best be described as 'rattles' or 'tapping'. When a car stands overnight all the oil drains back into the sump (oil/pan).
There are two things (usually) that can be cause the rattle/tap:
1. Because the oil hasn't been pumped around the system, at start up worn big end bearings can rattle and tap on the crankshaft until the oil 'fills the gaps'. The tapping/rattling goes away as the engine warms and oil is pumped around the lubricating system.
A 'bottom end tapping' is a symptom of worn big ends (they are bearings at the bottom of the piston and fit around the crankshaft).
2. A rattle/tapping from the top of the engine can either be a worn camshaft or 'lazy tappets'. Again, when the engine warms and oil gets to the camshaft and tappets (also called 'hydraulic lifters) the noise will disappear.
If your car has this rattling/tapping noise - identify whether it is coming from just under the rocker box (ie the camshaft/tappets..) or the bottom end of the engine (big end bearings).
If the noise is coming from the top of the engine, try an oil change with a can of thick 'additive' included. A lazy tappet (lifter) isn't too much to worry about. A worn camshaft will affect the performance of the engine, though continue to do its job. An oil change with an additive included may help in quitening things down.
A bottom end tap/rattle (or 'knock') - the sooner that is sorted out the better.
It's called piston slap, what happens is that when the engine start to get a few more miles in it's life. The clearance between the piston and cylinder walls are greater then when the piston are warmed up and has expanded.
You can add Lucas oil treatment to you engine oil to put a film of oil along the cylinder walls, so when you start the engine there is a coating of oil there that will help your engine to last longer. Just follow the instructions and try not to drive the Tahoe until the engine has warmed up a bit, the winter will be more noticeable and will take longer for the piston slap to go away.
Gm has a up graded program to address the piston slap to help make the engine last longer. Believe it's covered under the TSB if you bring it in to have it addressed. The program simply turns the timing back on the engine when it's cold to help eliminate most of the knocking and is helpful in making the engine last longer. As the engine warms up, the program brings the timing back to where it should be to not economy and performance is lost.
Thank you for using fixya and good luck.
If it is coming from the top of the motor, I would say it is a lifter tapping. If the sound is coming from the lower end of the motor I would say you have a rod knocking. If it is alifter you can replace just that lifter, if it is the rod I would consider a rebuild.
THIS IS NORMAL noise for your truck. carbon buildup on pistons causes a cold start knock until warms up. you can run some top engine cleaner thru engine to help. but noise is nothing to affect life of engine