Anyone considered that it may *not* be the fan after all?
I found this thread because I too was looking for confirmation whether the fan noise I hear on my 2012 iMac is normal or not.
I used to own a high-end late 2009 model with 1000 rpm fans - nothing to hear. New 2012 iMac (680MX, Core i7) has a constant hissing noise. Not very audible, the clicks of mouse & keyboard are far louder. Though I'm really sensitive thanks to no outside audio pollution. I can even hear the humming of my TV LCD screen on mute.
So … after playing around with the fan speed (iStat) and having had plently of hard drive models to work with recently, I suspect that the noise most of us are hearing may actually be the spinning of the hard drive!
Why? Because the sound the fan makes as it speeds up seems to shift or change the "type" of noise generated. Though the more I speed up the fan, it doesn't really change its audio characteristics. It's only when it falls below 1500 rpm that I start to hear more and more of the constant hissing noise I hear all the time.
What's more, the sound at the back has the profile of a running fan. There's a slight ffft-ffft-ffft sound of the fan blades spinning and air pressure constantly rising and falling. That's not what I hear at all on the front: at the front it is a very constant humming/hissing sound, no flapping blades.
Think about it: a 3.5" 5400 rpm hard drive spinning has a constant, low-level hiss that most people would dismiss as barely audible. The hard disk sound can be enhanced depending on how the fan and its casing are connected and positioned.
And the fact that we may actually be hearing the hard disk may have two explanations:
- The new model's casing may allow a better transfer of noise from the hard disk, possibly to the front thanks to the much thinner glass. I can hear the noise sitting in front of it, about 40 cm away.
- The air vent is where the air is blown out - naturally that's also where most any noise coming from inside will come from. If you listen closely there you'll of course attribute the noise to the fan. But both loudness and vibration of the sound on the back don't match what I hear on the front.
Possibly the only way to confirm would be to open up the iMac, and stop the fan altogether. See if the noise persists. Anyone care to try?
Btw: if the iMac is standing on a small wooden or glass table the iMac may give off more sound than if you put its stand on a piece of cloth, carpet or plastic. More so if its against the back of a solid wall - the noise gets reflected back on you. Even the stand itself influences the sound, I can clearly hear the sound profile changing depending on what angle the screen is on.
It may be easiest if you simply find a piece of old carpet or kork to place your iMac on, perhaps even cover half a square meter of the wall behind the iMac. This may be enough to dampen the noise significantly. I'll try this myself soon.