This is not clarified in NC law. NC has a general prohibition against carrying concealed weapons. Which means that there is technically (and legally) some latitude for a subjective interpretation.
Take a look at the NC AG letter, page 25 of the link I previously posted, for this:
"It is unlawful to transport a weapon (absent a proper permit) that is BOTH concealed and readily accessible to a person."
Also, in that same paragraph:
"Obviously, a weapon would be concealed and readily accessible, and therefore in violation of North Carolina Law, if it were placed in such areas of a vehicle as under the seat of the automobile; in a bag in the back seat; or in some other manner is covered or hidden within easy reach of an occupant of the vehicle."
If the rifle is openly laying across the back seat, then it's not concealed. Depending on how one views accessibility, it may be considered readily accessible. But it's not both. If it's openly visible, you could have it in the front seat, next to you, and that would be OK.
If the rifle is in a gun case in the back seat, then it's "concealed" with respect to "not plainly visible". However, it's not "readily accessible" in such a position in such a gun case. Also, a case of any kind that is clearly recognizable as a gun case (or sleeve or zippered rifle pouch) may also obviate the "concealed" aspect.
Now, that said...NOTHING I've posted can be considered definitive legal guidance...I'm not an attorney, and even if I were, I'm not YOUR attorney.
An officer can cite a person for nearly any violation, regardless of what the laws may say. The real question is whether or not that will hold up in court.
However, in general...typical common sense transportation of a rifle to and from a shooting range (or hunting) takes care of this. If anybody has any doubts, then simply make sure it's not BOTH concealed and readily accessible.
NC is a "must inform" state, with respect to concealed carry. Which means you're supposed to inform an officer you're interacting with if you're carrying concealed. With open carry, or open view, there is no need to "inform" because he already knows. However, common courtesy, and sensible precautions, apply as you see fit when you're transporting a rifle in open view.
Just remember...think before you engage your mouth. Starting off with "I HAVE A GUN" would be what we call "the wrong foot". Be smart...start off with something more along the lines of "I'm going target shooting at the range and I have a rifle in the back seat."