On the 4 class 777 configuration, 2A and 4A have a noisy air outlet (or something similar) in the panel above the seat, that is only on that side of the aircraft. It emits a quite distinct and noticeable fan noise, clearly audible above the general aircraft noise, especially when the seat is fully upright and one's head is directly below it.

On one recent flight I found the noise so disturbing, that I changed seats, and I am now avoiding these seats altogther whenever possible.

I asked the CSD what it was but she had no idea: "Oh I have never noticed that"

Does anyone know what it is and why it needs to be where it is ? Also, why is it only on that side of the aircraft ??