Speakers have strong magnetic draw, BUT.. their magnetic fields dont extend out too far. Example, it's not like you can hold a pair of scissors a cm away from your sub and you can feel the speaker's magnet pulling it. You should keep it a bit away from speakers because if someone knocks the speaker and it comes into close enough contact with the hard disk. THEN.. it's bye bye data!

Of course.. if your speaker falls on your 360 you have other thigns to worry about lar