Auto-wake from hibernation

Can anyone tell me why my new Inspiron M5010 wakes itself up from hibernation?  And what I can do to avoid it?  I'm not mistaking "hibernation" for the "sleep" mode, in which the "on" light remains on and the power button light "breathes."  In hibernation, everything goes dark and I assume the machine is off.  But suddenly it will wake itself up when I'm nowhere near it.  I'd rather not power down entirely.