I changed the pump and it does sound much quieter than before, but it still isn't perfect.

I think you may be onto something with the ID. I am using an aftermarket hose that was on the car, got the pieces from John and just put them in. They went in remarkably easy and didn't bind on the sides of the hose in the slightest. My logic there, which has been known to be highly subject, is that if the pieces aren't tight around the side, they would allow some of the damping properties to be reduced thus making the sound quieter without getting rid of it completely. Good point.

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1980 300TD, SOLD
1984 300TD, 275K
1999 C230 K Black & Tan
2013 C250 Black
1974 CJ5 Red
You might faint from the fight, but you're gonna find it. Every challenge could have paradise behind it. -John Popper-