Freezing ps3 when stationary...

Ok I know this is going to seem weird but anytime I leave my ps3 on in free roam defiance and dont move for more than 30 mins it freezes without a doubt , I've don't it 4 times in a row just to see and it froze all 4 times , now it don't bother me what so ever cause when I play for long sessions on it , it hardly ever freezes , anyone else noticed this ? Reminds me of fallout 3 that did it too

Mine randomly will freeze when it feels like it, however I've left it on sitting in a town for about an hr once without it freezing.

i'll test it later see if the same happens for me..