I don't see anything wrong with the stand. Is it possible it is just settling as it is new? I have gone under the house and nothing looks any different than it always has.
I'll be honest with you, I've never heard of a "settling in" period for an aquarium stand. With the weight involved it really needs to be right from the get go. Sitting there watching tele whilst it's creaking away must be very unnerving.
If everything looks ok then all you can do is give it a bit of time, maybe contact the manufacturers with your concerns. The alarm bells may ring for them and they may replace it, who knows.
I wish you luck, and keep us posted.