Welcome to my world!! I've been dealing with a hummer/singer in my office for MONTHS (almost a full year) now. I tell (or ask) him to stop. Finally at our last company staff meeting it was mentioned not to do that because it is distracting to those trying to concentrate. And he still does it! But I just remind him of the meeting. I actually haven't heard him today, now that I think about it.

A co-worker that used to sit in the cubicle right next to him would wear ear plugs or headphones to drown him out. And I think it's worse because he is male, so the sound is deeper and travels farther.

Good luck! I would definitely tell HR though. I did! And I told my supervisor and she told me I should talk to him and I told her I DO!!!