Sounds like you have all the bases covered. Changing a oil pump on a 17 year old engine is a good idea. Some of the guys here have suggested to me to take off valve cover and look down inside and see if chain guides are intact. While your there, adjust valves. If that doesn't stop the noise then you gotta go further. I have read that a chain tensioner thats bolted on too tight will make a strange noise and might stick in a retracted position, making the chain slack on decelaration. If you replace t-chain, and find that timing cover has a groove from chain, it can be welded. That will prevent possible coolant leaks later.

Good luck.

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