The more we increase the amount of decibels of a sound, the more power behind the sound from the sound source. A good example is that if you play a song really loud on a set of speakers, when you turn it up to its loudest, it is likely that you will feel a certain amount of pressure coming from the sound source.

This is applicable to the big bang, with a loud sound comes a significant force due to the power of the sound, of course it does depend on the source.

So in answer to the original question, it is likely that there is a sound so loud that we couldn't hear it because if it were so immense it would have already burst our ear drums by the initial force, but it could go either way, there may be a split second in which you hear the sound before the pressure cripples your ear drums or the pressure may be so overwhelming that your ear drums pack in before you have chance to perceive the sound.

To the extent where a sound so loud could kill someone, its definitely possible, as i said above, with loud sound comes great pressure/force and if the sound produced was so powerful it would likely mean it produces a lot of pressure, if this pressure is significant enough if could potentially either crush the body, or maybe soft organs such as the brain thus rendering us dead.