Hi All
There's a simple solution to this, if you know about the inside of a computer. DO NOT follow these instructions if you don't feel comfy working 'inisde' a computer.
So I have the same issue with 13" MBA. After about one week of working with the new Air, hizzing sound comes from the back left side of the Keyboard. I use iStatPro and theres a correlation between the hizzing sounds noise level and the fan rmp. Ok, it is also not normal, as I did some video editing on it in the week it still sounded normal, the fans went up all the way to 6500rpm without the ticking sound.
*The only way to fix it yourself it to open up the machine with the special screwdriver,lift the fan out, clean it with air pressure, put a small amount of machine oil on it, and put your MBA back together.*
Of course, this can void warranty, and you should not do this if you haven't done this before.
The cause of this issue has to to with fine dust or small pieces of hair being sucked inside the MBA via the keyboard or the right back side of the keyboard, which eventually get's stuck in the fan.
This is the screwdriver you need:
http://www.ifixit.com/Tools/MacBook-Air-5-Point-Screwdriver/IF145-090
Hope this helps
Love
Julez