Hi.
maybe you can use a animation event :
place a fsm on the object with the animator.
if you have more than 1 fsm on that object, make sure its on the top (as it will use the 1st fsm it sees)
add a event to your animation on the spot where the foot is lowest.
select the event and on the inspector, select "Set State" or "Send Event"
then place the 'State Name' or transition event name
set state seems to work faster than send event, but both should work.
in the state, do the sound or whatever you need.