I had a 2001 Nissan Altima in for an oil change, and I noticed a noise coming from the engine. It was little bit like a rod knock, but higher pitched and higher up in the engine.

Looking in the oil cap you can see a hint to the problem. It should be a light to dark brown color inside, but there’s a grey tint to the oil. That is caused by tiny metal particles from the camshaft or other valvetrain components as it slowly wears itself to death, also causing that knocking noise. It’s possible for the engine to run a long time with this problem, but it’d be best to replace the head if planning on keeping the car for a while.

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-Dan