I've got the 97 F350 and I also put the HPX crossover on. It is designed to equalize oil pressure across the two banks of cylinders, especially that #8 on the rear drivers side. The noise is referred to as "cackle". Aklim has a point too on the air in the fuel lines. You can go through and change out the connectors, make them air tight, may relieve some of the noise. Or you could just go buy some god-awful giant exhaust, straight pipe it and drown out any other noise there might be.

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-livin' in the terminally flippant zone