Noisy Overflow - Help Please!

[Ron99]

I am finally trying to get the new 65 gallon tank set up. It is drilled in the upper left corner for an external durso overflow. I have it built and set up but it is very noisy sounding like rushing water and also gurgling quite a bit. It is not flushing and the water level in the overflow box stays the same. it is just sucking alot of air and gurgling quite a bit.

I tried putting a reverse durso on the outlet at the sump but that does not seem to have helped at all.

Any suggestions would be greatly appreciated.