That's interesting. I have the same exact issue and whenever I tell people about it they think I am crazy. I don't have a problem with people chewing food when it's lunch break and we sit in the cafeteria, but man, when I try to focus it kills my brain. Just last week the guy next to me started eating kind of late in the day (where my brain was almost empty). I then tried to cancel it out with headphones, but that just wasn't possible anymore.
And I still don't know how to deal with it. Sometimes I try to take a walk for 5 minutes and it helps, but not always. On some days I get a full mental breakdown because I get angry at myself getting angry on somebody just making noises any normal human being does while eating