Open string loud buzz

A couple of my guitars had the buzz when I hit a bit to hard on an open string.
Looking over the strings and taking some close up eye ball inspection I see the strings almost touch the first and second fret bar.
I cured that by shimming the nut and they both sound great but one guitar has the same problem.
I can't remove the nut because it seems to be a part of the white plastic trim that runs down both sides of the neck.
It looks like i'm going to have to cut it but want some suggestions first.
Appreciate any suggestions on cutting the nut.
Thanks BOB LECH AF2Q

An easy way to shim a string is to put a thin strip of some fine grain sandpaper in the nut under the string, face down with the grit on the nut.

Does that help?

http://www.fretnotguitarrepair.com/repair/acoustic-guitar/nut.php

Thus will help you out.