Check the sparkplugs for tightness. I just had a coil go out so I brought in to my mech for service. When we pulled the covers off the sparkplug gallery you could hear a knocking, that would disappear with the covers on. I had him replace he plugs while it was in. He found that at some point in the past they had been replaced. Two of them where only hand tight
I was getting blowby oil past the plugs
Could have been really bad if one had backed out enough to blowout and strip threads.

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2003 X5 4.6is Estoril Blue
2005 Infiniti G35X
1972 Datsun 240Z
1991 Isuzu Impulse XS Sold
1972 Fiat 850 Spyder Donated
1972 Datsun 240Z Sold
1972 Datsun 510 Sold