does it always rattle at an idle?are you sure the noise is from the top of the engine?
this may be caused by dirty lifters
you can buy an additive at your local partsstore to add to the oil and will help clean the lifters
we,here at my shop,use automatic transmission fluid for this,,we add 1/2 quart of atf to the oil and just drive it,,,,atf is high in detergent and works well for this
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