Disc brake rotor scraping against mounting bracket
A few things can cause this:


In theory it could be a problem with the alignment of the mounting posts on the fork. This isn't likely for a few reasons. One is that the problem would have been pretty egregious if the bike was doing it from day one, i.e. the wheel wouldn't have turned and someone would have noticed. Another is that suspension forks rarely have such problems because the brake mount is usually part of the same casting as the dropout, and in that case you're not going to have random one-off problems with bad positioning of the mounts due to fixturing errors at the factory, which does sometimes happen with frames.
A sufficiently out of true rotor could do this.
If the wheel were installed out of alignment in the fork and ridden it could cause this.
If the hub parts were put together wrong, after service for example, it could do this by creating an incorrect distance between the rotor surface and the left locknut service. Between the plane of the back shoulder area of the centerlock mount and the plane of the left dropout should be about 19.5mm. If this happened, it would also throw off the wheel dish unless that was corrected afterward to compensate.