Brand New 27" iMac: humming noise!

It should be dead quiet. Contact AppleCare immediately, the phone number is in your owners manual.

Regards,

Roger

I agree with Roger - I bought the very same machine on Tuesday and I can't hear it at all.

How loud is the hum? I have one just the same save mine is an i5 2.2 quad and I have a hum..in fact as I type the rest of the house is asleep but my imac is low level humming

It kind of depends on where the noise is coming from. If it's anywhere in the top left quadrant of the screen, definitely take it back or get it fixed. It's probably not dangerous to leave for a day or two, but I wouldn't really chance it. If the display itself seems to be making noise... That's annoying but not really anything you need to worry about immediately.

But during normal operations, like not playing games or anything stressful such as that, the iMac should be pretty much silent.

I got my 27" 2.88 i5 yesterday, and does definitly not hum. There is a soft tapping noise which seems to come from the hard disk , but apart from that it's very quiet. To hear the fans you have to put your ear right over the ventilation slot at the top rear - careful not to burn your ear though - but thats another discussion 😉

When I first got my new iMac last October my wife could hear a persistent humming noise that she reckoned was really loud - I couldn't hear a thing, although I've got good hearing. Must be something do do with us hearing different frequencies. Anyway, after a couple of days she turned around and declared that the irritating humming sound had stopped.
Maybe it'll cure itself in a day or so, if not a phone call to Apple I guess.

There are two power supplies in the iMac starting with the Late 2009 models. One is the main power supply, the other steps up the voltage for the LED backlighting. The main PSU is a bit left of center on the top of the system, the other one runs along the left edge from pretty close to the top to about the middle of the system. One of those is likely defective.

While I'd put the odds as pretty low, the worst case scenario would be one of those catching fire and completely destroying the computer.

I'm no electrical engineer, so if there are any out there who want to disagree with what I'm about to say, I'd definitely defer to them. But I'd say the humming is probably a sign that the PSU is not having it's power flow regulated properly and somewhere there's a buildup/backup of energy. It could also be a lack of proper shielding that's creating a kind of sympathetic resonance. Lots of possibilities, but so long as the frequency/pitch of the sound is remaining constant... PROBABLY nothing to worry about in the next 2-3 days.

Again, I'll defer to any electrical engineers in the audience, but having worked as a hardware tech for around 2 years, I've run across people who have had loud PSUs for years with no obvious ill effects. I wouldn't recommend it myself, but there's at least anecdotal evidence to suggest it's more of an annoyance than anything.

There's a small chance, but I'd say it's highly unlikely. The PSU's are all solid state components, so being tossed around a bit shouldn't really hurt them.

And what they had you do was a SMC reset. I would be quite surprised if that had solved the issue, but I suppose it was worth a try given it only takes a few seconds.

Yours is a pretty classic case of a manufacturing defect. It happens. I would recommend that before you return the system you first make sure you have a backup of any files you may have created in the short time of owning it. Then boot off the install DVD and load up Disk Utility. From there, I'd recommend doing a drive erase, and at a minimum selecting to zero out the drive. That should make it pretty hard for someone to recover any data should they decide to get nosy and start snooping around. Maybe do this the night before the system is set to be collected. Even selecting the 7-pass option. It will not likely finish overnight, but it will have made probably 2-3 passes in that time and you can just stop after that and reinstall the OS, which will further obliterate a lot of data.