I have ADHD and as such have terrible difficulty maintaining my concentration, especially when working on homework. Because of this, I often like to work on the "quiet floor" of my university's library. This floor is basically supposed to be silent, though there is no authority to enforce this.
Recently, every time I have tried to work there, there has been a person on the quiet floor who clears their throat about once every two minutes. The noise is quite jarring, and can be heard from far away. I have tried wearing headphones, but have to listen to white noise rather than music to concentrate, and even with headphones on, their noise is audible (if only faintly). Moving to another location on the floor is not an option since there are often few desks open, and I have to take what I can get. Often they are audible from other places on the floor anyway. Similarly, I have problems concentrating in other locations on campus.
How can I tactfully inform this person that their incessant throat clearing is incredibly distracting? If it was occasional or quiet, I could tolerate it, but since it is extremely frequent and quite loud, I feel like I am losing my mind trying to ignore it.