Quote:
Originally Posted by KarTek
I'm hearing a quiet "tocking" sound from the top side of the engine that seems to correspond to one cylinder. It's not a rod knock but more of what I imagine a weak lifter might sound like. I'm also hearing a slight "woofing" from the exhaust that is timed perfectly with the noise in the valve train.
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Have a look at missfire counts, you might be having an arcing coil / boot.
If you do see a cyl with higher than average missfire counts, move that coil / boot to another cylinder and see if the problem follows.
Past that I'd vote for a collapsing valve lifter / lash adjuster, a tight valve guide or even a broken valve spring.
Someone on this site used an audio recorder with a mic on on channel and a cylinder pulse on the other. ( Or did something similar ) They then put this through audio edit SW and located the point in time when the noise occurred. At that point they figured out what was moving to zero in on the noise.