I'm having the same problem at my job. People always speak loudly around my office, even if I ask them politely to be carefull.
I'm pretty sure humming should be avoided since some find it "passive-agressive" or disrepectful (even if talking loud is more disrespectful in my opinion).
After trying a lot of headphones, I finaly found some that are doing a great job at noise canceling. You should look for tight fitting earbuds. When it gets noisy, I use them to play some smooth music and really cannot hear anything. Both my productivity and my relation with my coworkers improved since!