Engine making a slight rattling or pinging noise

when engine get warm oil get thinner so it can leak from a small hole
belt will make noise on dry pulley change belt

Lifter noise is typical of an oil pressure issue, or when oil channels are clogged from infrequent oil changes.
You can start by changing the oil and REPLACING THE FILTER. Marvel Mystery Oil or other oil treatments will help clean the oil system and quiet the lifters. If an oil change and crankcase oil additive helps quiet the noise, change your oil every 500 miles for at least 2000 miles, and the lifter noise is likely to stop.
Are you getting a CHECK ENGINE light, or an OIL PRESSURE warning? Have ODB codes checked, and be prepared to replace the oil pump or oil pickup tube, especially if the car has over 150,000 miles. Once you have correct the issue, change oil more frequently.

Your hearing lifter noise common in most cars in cold weather I have a 2001 sc1 same engine as yours here's how to get rid of that ticking sound go buy a quart of Lucas synthetic motor treatment change your oil and leave it 1 quart low add the Lucas synthetic oil stabilizer within 1 week you will not hear the noise agian reason your hearing the noise is there's no oil at the top of the engine on a cold start oil when cold is thicker hints why your noise in your engine what Lucas does is eliminate the dry start by the way my engine has 288,000 and does not use a drop of oil after you use this product you should use it every oil change you will see your car will thank you regards Chris

Could be engine "ping" from bad octane in your gas. Try a gas treatment like STP octane boost. If is still does this, check your oil, bad rods or low oil can make this sound too. Try Rislone for oil treatment or Slick 50.

there are only so many ways for gas to get into the oil.one someone purposely pured gas into the crankcase.two the engine is running very rich and not able to burn the excess gas,three the fuel pump is leaking gas into the crankcase,four the oil has not been changed regularly and the gas has thinned out to the point that it cannot seal the engine from the gas that normally is burned in the combustion chamber.If maintenance is regularly performed that fixes #4,I doubt that anyone would pour gas into the crankcase especially at the price of gas that fixes #1,if the carburetor is working as it was designed to then that eliminates running rich and fixes #2.if the above is good then the only thing left the fuel pump, can leak fuel into the crankcase and they won`t make noise necessarily.as far as the slight pinging one of two things can cause this, the engine is running slightly lean and or the timing is too advanced and needs to be reset to specs

You problem is most likely just lifter noise. This is common with a lot of Ford engines with self adjusting lifters. Although lifter noise is bothersome it doesn't pose a serious problem. Unless your engine starts to miss or your gas mileage drops way off lifter noise is just an annoying problem.
I would recommend that you add some Sea Foam Engine Treatment($6-$8) to your oil. This is not an oil treatment it's more of an engine cleaner. If this works you'll need to add it every 2nd or 3rd oil change.
If this doesn't take care of the problem then depending on your engine you may have adjustable rockers that would allow you to remedy the problem. If not, your options are limited to living with it or replacing the lifters and possibly other valve train parts.

The gas could of lost some of its octane which will cause a pinging or rattling noise try oil change and fresh gas.

The 2.2 or 2200 four cylinder engine is bad for lifter rattle after the mileage gets up there, timing gears are also noisy in them.. I have had good luck using full synthetic oil, I would buy an engine oil flush kit with the next oil change and then use synthetic, If this noise isnt consistant with engine speed, then i would look at pumps and pulleys on the fron of the motor, sometimes AC pump clutches get squeeky and often rattle when disingaged, try turning the AC or defroster on and of to test for a change in the noise.

how many miles on it,sounds like lifter noise which is normal for high mileage jeeps,but if you have over 140k it is not a good idea to run synthetic oils as they are thinner than conv oil and it might start to consume oil.

oil shouldn't cause this symptom. (syn. oil and reg. oil - their is only a 1 percent difference between them) a rattle noise could be a valve rocker arm OR (the rattle i had) the catylitic converter. the honey comb stuff broke up into pieces inside.