Just installed a 700 kit, this thing sounds like Niagra falls. Its a nice kit, I have lots of pics, but its hands down the loudest drain I have heard. there is no gulping, but the sound is similar to just having a 1 1/2" straight drain pipe free falling water. And to top it off, this morning my Nano light caught on fire and burned the canopy. Cant wait till my wife gets home.... new tank-with extremly loud drain topped off with the smell of burnt plastic in our house...Great....My cellphone will be ringing off the hook ! haha
Its a drain kit with a durso? If so try adjusting the air vent.
Also try adjusting the flow rate of your return down a bit...assuming you have a valve on the return output.
A new drain is always noiser than an older drain...at least you can tell your wife that. Once they get some biofilm they seem to quiet down some at least in my experience. But there are probably some other adjustments that you can do as well...
I usually always put valves on my supply and return lines, but i did not this time, just so i could acheive as much water flow as possible. But I think i might have to choke it a bit with a valve. its annoying.