yeah, I learned long ago with some LCDs at work to NEVER expect LCDs to get better. We got a few in (Thankfully none I had to use) with some weird uneven lines of pixels... it was hardly noticable, no one saw it but me, so we ended up keeping the monitors.. and they got worse and worse.
I've seen other LCDs with weird shimmering/interference sort of things (Even in DVI)-- again, didn't seem bad at the time, but got worse as time went on.
I agree to return the monitor.. and keep doing it until you get one that's perfect, out of the box. It's not hard to do, although the people at the store may learn to hate you.
(one I had Best Buy hook up a replacement to a store PC and I went over it for about 5 minutes before taking it-- still using that monitor today 4 years later, been great! [knock on wood])