A very good article about new MacBook Pro's stupid audio/video playback problem.
Intermittent lag when viewing video clips. It would happen every couple of minutes and would last for approx 5-10 seconds. During that time, the video became VERY choppy and the audio began stuttering with a strange echo.
Go into device manager (see below for how to get there) and double click your wireless network adapter. Now go to the “Advanced” tab. Scroll down the list to the “Disable Band” item and single left click on it. In the options drop-down panel on the right, select the 802.11a band to DISABLE it.