You should post whether or not you have the SSD drive. If the problem is really related to the HD, then I guess no one should have that problem with the SSD version.
Using people's signatures, we can see that 1.6/80 and 1.8/80 models have been affected, but afaik, no one reported the sound on a 64GB SSD model.
This has happened to me several times (more than 10)
Everytime it happens I take another backup of the disk with time machine. I am convinced it is my hard drive slowly dying on me.
Read somewhere that it is suppoosed to be completeley normal on these drives and nothing to worry about, but I have never in my 20+ years working with computers ever heard a healthy HD making that sound....
I have 1.8 with traditional HD
I also always have my speaker muted so it is definately not coming from that...
I have heard the same noise once on my beloved MacBook Air 1.6/80. I had it on my lap at about a 45-degree angle, similar to an above user's retelling. My educated guess (as a digital hardware engineer) would be that it comes from the hard drive head servo during some particular recalibrate/error correction cycle. They're called "voice coils" for a reason! Although the much-more-common calibration "clicking" noise and this rare shriek (for lack of a better term) are unnerving, I'll bet there's nothing actually wrong with the drive. The SMART status is fine, so the drive doesn't seem to think anything is wrong. The tiny Samsung drive is just noisy.
Make that another one with a new MacBook Air with that experience.
I actually looked around the net quite a lot before finding this thread and I'm so relieved to find that I'm not the only one to which this has happened.
My HD is the standard with 80GB of space.
I'm on my 2nd Air now. This one did the same sound once too. But I'm not all that worried about it anymore. It would be cool to get a real explanation of it though.
This same thing happened to me twice on my 5G iPod actually; it is scary sounding. Even though the first time happened a week into owning it, which must have been 2.5 years ago now, it still runs strong. So don't be too scared about your drive dying because of it.
I had the same sound recently. I agree with the other posters who said it was 'scary'. Quite unnerving, I've never heard anything like it in all my Mac years.
It happened shortly after a restart and whilst backing up to Time Capsule wirelessly and not plugged into the power lead.
I've had this about 3-4 times since I bought it in February. It pisses me off that it occurs completely at random, and I've no hope of reproducing it at the Apple store.
Thank God for Time Capsule auto backup. With it's clicking and screeching antics, this HD will fail prematurely, I'm sure of it.
SSD here -- and I have never heard this loud screeching noise. Hope I never do! Chances are that since mine is the flash drive that I probably wouldn't.....
I hope someone can eventually find out what this is and what the cause is....
Mine has done this a few times since I bought it about a month ago. Doesnt usually freak me out to bad, but it is definitely something I've never heard before on a laptop
It's exactly like the youtube video.
I'm waiting for the day it does it in class this fall and then I'm going to raise hell at the apple store.