New TV, picture is great but a transparent line moves up through the picture.

If it's new, I'd return/exchange the TV.

If you can't return/exchange it because it's too late, then double check other inputs/channels. If it happens on other inputs with different devices, then there is something electronically wrong with the TV and you will most likely have to call a repair tech or take it somewhere to be fixed. If under manufacturer's warranty, you'll obviously want to call them.