Apple Thunderbolt display and MacBook Air plagued by noise
updated 10:50 pm EDT, Mon July 16, 2012
Bug temporarily rectified by disconnecting display
Some users of Apple's Thunderbolt display and the new 2012 MacBook Air line have discovered that after a few hours use, the display's speakers distort, crackle, and emit a static noise. There are no permanent solutions, and temporary fixes include disconnecting the Thunderbolt cable and replugging, or changing output methods away from and back to the display's speakers. Apple has no official response on the issue as of yet.
The problem isn't universal, but a six-page thread (with similar other comments started by other users) on the Apple support forums detail the hardware configurations and running software from various users that are running into the problem with the display and new laptop. There doesn't seem to be any induction by a specific software package, and a logical or physical disconnect of the display seems to work to rectify the static for a time.
During initial review and testing by Anandtech, the Promise Pegasus storage enclosure generated a similar, but not identical, phenomenon in the Thunderbolt display. Similar, but not identical, methods fixed the problem -- the application using the audio would function fine with no distortion temporarily after a quit and relaunch. Further testing demonstrated that short bursts of writes using Thunderbolt caused no static, nor did large data transfers using other methods such as the Gigabit Ethernet, FireWire 800, or USB 2.0 ports on the display. No data corruption occurred during the periods of static with a large USB transfer in parallel with audio playback.
An independent testing laboratory MacNN has consulted before was queried, and they confirmed the phenomenon on one of two 2012 MacBook Air 11-inch laptops with default software in an "out of the box" condition. A ground-fault was injected on both setups, and it neither started the static on the one MacBook Air that was known to have manifested it, nor induced it on the unit that was trouble-free.
Strictly regulated power as well as "dirty" power in several degrees was connected to both displays and laptops, and the timing to static on the speakers was unaffected. While just plugging in a USB sound card into the Thunderbolt display still manifested the static, the laboratory confirmed Anandtech's conclusion that connecting a USB sound card to a USB hub, connected to the thunderbolt display prevents the development of the unwanted noise.
MacNN spoke with an Apple Genius supervisor at a flagship Apple Store, and they are aware of the problem and its periodicity, saying that it affects "a small, but not zero, cross-section of users of both devices." Little information is available at this time to come to any solid conclusions, but continued testing and user reports may assist in coming up with a permanent solution.
