The dull knock is caused by the phasers. They were redesigned in 2006 and can be identified by a "L" and "R" for the timing marks. The original phasers have a "L" and "l" fot the marks. The updated VCT solenoids wont hurt anything but with 163k I would recommend taking the timing cover off and replacing the chain tensioners and guides. The tensioners have a small rubber seal that seals to the head and every one that I have removed have had a blown out seal. That bleeds off oil pressure and can cause excessive wear on the chain guides. So new phasers, VCT solenoids, chain tensioners, and guides and you have almost addressed every failure point on the engine and should last another 163k miles
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