Legendary Ninja Warrior, Baba Da Rahto, learned early the importance of running quietly.
To be invisible in a race cannot be overemphasized.
So how does one run quietly?
If there are stairs involved in the race, keep close to the wall and go on your toes only. Even better get on all fours while ascending or descending, if you can do it unnoticed.
Distribute your weight evenly.
Softly touch the ground, mid-foot, engaging the calf muscles for strength and stabilization.
Develop a habit of being constantly aware of your movements throughout the day. When you hear yourself doing something, find out the cause of the noise and try it again more quietly.
As you continue to train, you will become more aware of your body and it's noises. Remember the creed of the Ninja Runner -
Train hard and run soundlessly.