I have suffered with a noisy fan for the past two years whenever I plugged into my Thunderbold display. I have finally solved the problem. I sold my MacBook Air to a friend who does not have a thunderbolt display. She is happy as her the fan never starts up. I bought a new MacBook Air - the G7 with 8 gigabytes of RAM. Now my computer is silent all the time. There is nothing I can do to get the fan to start up when I'm plugged into my Thunderbolt display. It doesn't matter how many apps I have open my computer stays silent.
Apple has not been helpful in solving my problem. Initially the the staff of my local mac store denied it was a problem. They told me my computer was fine and the fan was supposed to come on to cool my computer. When I went to buy my new computer I asked whether I would have a problem with the fan. They told my that a new computer would not solve my problem. I asked the salesperson to check with the "genius" and he confirmed that more power (the G7 chip) and more RAM (8 gigabytes) were unilkely to make a difference in the fan noise.
Well Apple was wrong. I have a beautifully silent computer when I'm plugged into my Thunderbolt. It was an expensive solution but I'm happy. Apple needs to give it's head a shake on this issue.
Jo Hauser