One more thought then, when you have the valve open all the way and get noise at the drain are you talking where the water enters the pipe to be taken to the sump (top of the stand pipe)? I would get a sucking sound at the top of my stand pipe when I was first setting it up and found that I just needed to enlarge the air hole at the top of the tee fitting, I ended up with a 1/4" hole before it stayed quiet.
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