Unfortunately...it seems that I deleted the picture after the problem was fixed... but...
https://forums.macrumors.com/threads/1299177/
I believe I know exactly what you're talking about. Do you notice any bumps or dents at the hinge area right above the function keys?
For me, when they replaced they lid/screen - they used a screen that had too short of a wire (how the hell does that happen, I do not know). What you are likely seeing is that wire. It normally runs inside, right beneath the area between the hinge and the function keys. Because the wire was too short, they 'improvised' by shortening the distance the wire had to travel. This will cause a dent in bump in your case, since the case is not designed to accommodate the wire in that fashion.
That it back to the Apple Store. It sucks, i know - but this short wire issue is unacceptable. I COULD NOT believe they tried to pawn it off on me in hopes that I never notice. This can't really be an oversight, but blatant negligence / disregard by the people installing the screen (when installing anything into a computer, you KNOW when it does not fit right).
Edit --
Oh, if they try to 'fix it' without replacing the screen...you would likely get more issues (refer to the last picture in the thread I posted). The person who tried to repair it did their best - the wire became less noticeable...but the bottom casing bulged like no other. After a screen replacement, it was bad to normal.
Good luck.