Samsung 5084 w/ horizontal black line

I bought a Samsung 5084 11 days ago (Nov 19)- awesome first impression. Yesterday (Nov 28) I notice a horizontal black line on the screen about 6-8" from the top. No matter what the source- cable, antenna- the line is there. Turn the screen to all white, still there. I thought plasmas were immune to horizontal black lines, that such an annoyance was an LCD issue. Can anyone tell me what this is? Is there a fix or should I pull out the box and haul this piece back to the store for exchange? Many thanks for any advice as I am a full-blown rookie in this HDTV world.

Thanks for the responses. I took the set back to HHGregg and they exchanged it. Today was Day 10 since my purchase. The way I understood it, today was the last day of the 'you're covered for anything and can still get a refund' policy. I don't really know how to feel but right now I think the whole ordeal is a crock. You pay good money for a HDTV and after 9 days it has a problem. Lemon, bad luck, whatever, still a crock. I looked around the store and the sales guy showed me other examples of how plasmas go bad- snowy lines, bad panel sections, horizontal defects. To me, how can you afford to buy one of these TV's without the extended warranty? I hate to say it but I feel like by default you have to consider that cost when purchasing one of these sets. The cost may be high but what if after 13 months I'd had this same problem? I'd have a nice TV w/ a black line in it to show all my friends. You buy a plasma or LCD and it if lasts 9 days or 9 years, after that the defect is all yours. At least with a tube TV, if you couldn't stand the fact that the contrast was going south or some other issue, it only took a couple hundred bucks to replace. Maybe I'm just venting and revealing my ignorance- please, someone educate me. As long as this new one works, it is awesome, unbelievable, makes watching TV really cool. I'm just paranoid and don't like feeling like I'm waiting for the next failure.