Problems with media stopping and starting

I have recently become the proud owner of a MacBook Pro. As you will see from the below spec it is a decent machine and quite a new spec.

When playing audio through iTunes or VLC music stops and starts sometimes with pauses of 1 second.

I have closed all applications but the problem still persists. Checking available memory / cpu usage there is not visible reason why it should be doing this.

Can anybody please help me as this is driving me mad.

Hardware Overview:

Model Name: MacBook Pro
Model Identifier: MacBookPro8,2
Processor Name: Intel Core i7
Processor Speed: 2.2 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 6 MB
Memory: 4 GB
Boot ROM Version: MBP81.0047.B27
SMC Version (system): 1.69f3
Sudden Motion Sensor:
State: Enabled

Are you playing the music through a wireless network? I've noticed this problem recently as well. My media is on a Time Capsule which is played through a Mac in another room.

It seems that once in a while my network slows to the point where I get the behavior you describe. I think it happens when my non N network iPhone connects to the network.