ASSUMING NOTHING IS BROKEN....
A basic Eshops overflow box (or any similar "U-tube" design based on 1" plumbing) is going to be good for a max of 600 GPH and it will set the water level at the level where you have it's weir set.
So once you get it running quietly, you can adjust that weir level to your liking. The sump water level will vary some based on your adjustment.
This may require a smaller pump if you have no way to dial this one back. If this turns out to be the issue, then you'd really prefer to have a smaller pump anyway.
What size tank and what pump/model do you have?
A basic Eshops overflow box (or any similar "U-tube" design based on 1" plumbing) is going to be good for a max of 600 GPH and it will set the water level at the level where you have it's weir set.
So once you get it running quietly, you can adjust that weir level to your liking. The sump water level will vary some based on your adjustment.
This may require a smaller pump if you have no way to dial this one back. If this turns out to be the issue, then you'd really prefer to have a smaller pump anyway.
What size tank and what pump/model do you have?