Added AudioToolbox.framework to the project.
Wrote & implemented playSound inaction; wired to run button for testing.  ref. ViewController.h, ViewController.m, ViewController.xib
Wrote playSoundMethod, taking the sound file name as argument.
Unwired the playSound IBAction from the runButton.

ref. ViewController.h,  ViewController.m,  ViewController.xib
Implemented & tested playSoundMethod.  ref. ViewController.m
Implemented tick sound to count down prepTime.  playSoundMethod is called from the prepTimeMethod.  ref  ViewController.m