In an Apple Support Communities topic, users of new MacBooks Air launched during WWDC 2012 are complaining about a problem when the machines are used in conjunction with an Apple Thunderbolt Display.
According to the reports, users found that after a few hours, the sound from the Thunderbolt Display's speakers starts to distort, emitting static noise. Apparently, there is no solution that solves the problem, but some temporary options involve disconnecting and reconnecting the display cable or changing, momentarily, the audio output method.
The source of the problem has not yet been found, some speculate that it is linked to the use of the MagSafe to MagSafe 2 Converter, although there is no evidence. For the time being the team of Apple engineers has not commented on the matter, but it is certainly already aware of the problem.