Well can you isolate it to one side or the other. If you can, then you have narrowed your choices to 8 possiblilties. Try using a long piece of metal rod on the valve cover and the other end pressed near the front of your ear. Better yet, either borrow or buy a mechanics stethoscope and use that to try and locate the offending parts.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.