Hi there

In addition to what Cass_N says above: the issue that you have described is LED Lightbleed.  The LED lights are at the side of the screen and hence causing this.

As the TV is new, you could contact the retailer you got it from and arrange an exchange or repair. 

OR you could try simply 'cracking' the screws at the back of the TV.  What I mean is loosen them ever so slighly.  This issue could be caused by the screws are too tight and hence the LED lights and panel etc are squishing each other.

Cheers