I wonder when you start noticing sound delay? under 100 yards? The sound is just taking a while to reach your customer's ears because of the distance between him and the aircraft. If they broke the sound barrier he would know it (really know it).
Assuming speed of sound to be 750 miles/hour (and it is often slower due to atmospheric conditions), a little work with a calculator gives a speed of about 1,100 feet per second for those sound waves. So at 100 yards, you would have a little over .2 second delay.