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Isolating unusual engine noises is made easier using a hose. Move around the engine with the hose end with the other end to your ear.
To isolate/identify a spun con rod bearing, while the engine is running, short out one cylinder at a time on that bank by temporarily removing the spark plug wire from the cap. If the noise reduces/goes away on the shorted cylinder, that's the culprit.
As others suggest, could also be a worn rocker arm or rocker arm shaft. If the noise is from the chain box, could be an imminent chain tensioner failure, but the sound frequency is somewhat different from a rod knock as is excessive valve clearance.
Hope this helps.
Sherwood
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