I've taken over a code base that has subtle flaws - audio player goes mute, unlogged crashes, odd behavior, etc.

I found a way to provoke one instance of the problem and tracked it to this code snippet:

NSURL *soundURL = [NSURL fileURLWithPath:[[NSBundle mainBundle]
  pathForResource:[[soundsToPlay objectAtIndex:count] description] 
  ofType:@"mp3"]];
self.audioPlayer = nil;

self.audioPlayer = [[AVAudioPlayer alloc] 
  initWithContentsOfURL:soundURL error:nil];

self.audioPlayer.delegate = self;
AudioSessionSetActive(YES);
[audioPlayer play];

When I comment out the 2nd line (nil) and add a release to the end, this problem stops.

[self.audioPlayer release];

1. Where do I go from here?
2. Nils are used in a similar fashion throughout the code (and may cause similar problems) - is there a safe way to remove them?
3. I'm new to memory management - how can I discern proper nil usage from bad nil usage?