Wow, well I am not one to beat the slow down drum. But....... I would say that it probably has something to do with he amount of fish in a new tank, combine that with any die off you could have it you have any live rock and you got yourself a wharf my friend.
What do you feed and how often. Is there a possibility that the smell is from food and not the tank itself. I once had a jar of freeze dried krill that smelled like the 3 day old sushi. Even is you just opened it a crack the house smelled of it for hours!
Besides that I would say that the smell will most likely go away once you start a pattern of regular water changes and maintenance.
I hope the nitrate and nitrite or whatever it maybe are not off the chart. Since the tank is about 12 days old, I had taken a sample to the fish mart. Just last Sunday, they said the readings are fine. But caution not to put any more fish in there as it spike in several days.
As for live rocks, no I don't have any in there yet.