Just got this phone call. I recently signed up for job searches and also for some colleges which asked for my cell. If you did too then that might be a clue.
I have been receiving multiples calls from this number and the exact same thing is happening when I answer...humming noise and then on call back I get a busy signal. I Google the number and it came registered to two different people out of Oakland,CA. I know Metro PCS recycles there number pretty fast and all but this is crazy that there are so many people having it happen to them.