Hawgz, what we as humans hear and what animals in this case whitetails here is vastly different. There hearing is "more powerful" for a lack of a better term, fine tuned to there surroundings.

We have done it with our stickbows, and yes in most instances you are right, at 15 yards though there is a noise audible. No also understand a lower pitch travels farther then a higher pitch. A higher pitch travels faster. Whats that mean, some bows still have a thud to them, just low to our ears. In the case of hearing it from behind a saftey wall, this thump may or may not be adible, but rest assured, they can hear it!