lightning and thunder?

why is thunder associated with some lightning storms and not others ?  i have seen "lightning" only storms but no thunder.  why is that ?
and i dont want to hear about how far storms are....i have seen lightning close by and NOT heard thunder !

Thunder is caused by the heat from lightning. Although most lightning will produce thunder.  It is not always the case. This can can be the result of the to the composition of the gas i and moisture in the air.  The way the lightning bolt would heat the gas, sometimes the sound an be very faint.  Every once in a while, you can have a thunderstorm is is right on top of you with a lightning strike very close to where you are at and will hear nothing because the heat from the lightning bolt never generated a soundwave.  Therefore , you will se ethe lightning but never hear thunder.