I dont know anything about sumps!

[mr_alberta]

If you have a couple of holes already drilled in the corners, you could silicone a piece of glass in the corner as an overflow box and use the pre-drilled hole as the drain.

As to the noise issue, Willow is correct in that the majority of the noise comes from the spashing over the overflow and the water draining into the sump. Thus, if you have a lot of water moving to and from you sump, it can be trickier to quiet down.