Sporadic audio distortion on 24" iMac

[harikarikrishna]

Hi all, I've got a real puzzler of a problem and I'm hoping you can help!

I have a 24" Intel iMac, with the latest version of Snow Leopard. I bought it last July and have AppleCare. For as long as I can remember I have this problem with it:

* Every 30 seconds, almost to the second, the audio from the built in speakers distorts and gets slightly louder. This lasts about half a second then goes back to normal
* It only manifests through the internal speakers, it's fine through headphones
* Rebooting makes it go away temporarily
* I've reset PRAM and SMC to no avail
* I've tried turning Time Machine off to no avail
* I've taken it into my local Apple Service Centre, they couldn't replicate the problem, it only seems to happen in my house (every room I've tried it in is the same)
* I bought an expensive power filter/conditioner, this hasn't helped at all

I'm at my wits end with it! Please can one of you clever folk give me some suggestions?

Thanks!

 

[blackburn]

Shoot me but can you try bootcamping it and see if the problem persists? But if it only happens in your house it's weird, maybe interference from something? Since you bought and power filter, look for something that uses wireless
communication.

 

[harikarikrishna]

Thanks a lot for your reply! Bootcamping - what do you mean by that, running Windows on the machine to see if it's an OS X problem?

Good call with the wireless, I'll try running it off ethernet and see if that solves it...

 

[blackburn]

Your welcome Yep run windoze to see if the problem persists if it persists it's most likely interference or a hardware problem.

The built in wireless (wifi and bluetooth) it's supposed to be on and make no interference, look for other devices that use wireless transmission like a cordless phone.

 

[harikarikrishna]

One thing I forgot to mention - rebooting the machine solves the problem but only for a while. I sleep the mac all day when I'm at work and it seems the longer it goes without a reboot the louder/longer the distortion gets.

Also, I use a 13"macbook in the same location, from the same power source, using the same software and with the same hardware plugged in and it's never had this problem?

 

[blackburn]

That may happen due to a kext problem or a bug related to sleep, try to repair permissions and do a verify disk. Most likely it's an os x problem or an hardware problem.. Have you tried windows or linux? Guess it's faster booting an ubuntu live disk and see if the problem persists.

edit: Try another OS to rulle out if it's an hardware problem or an software problem

 

[harikarikrishna]

Not sure what a kext problem is, but I've tried verifying permissions and repairing the disk with no result.

I guess I'll try another OS on the machine, or boot from the OS X install CD to see if it's software or hardware, thanks for the tip.

 

[blackburn]

a kext is a kernel extension or like a module in linux or a driver in windows. the kext that controls your built in audio card might be bad, but try booting with linux or bootcamping windows to rule out if it's an os or hardware problem, I think it's easier than reinstalling os x, having written that have you already tried to reinstall os x?

edit: mrgoogle has already an thread on the apple board with the same issue that you have http://discussions.info.apple.com/thread.jspa?http://discussions.info.apple.com/thread.jspa?messageID=11240277 albeit no real solution

 

[harikarikrishna]

That's my thread!

I've not considered reinstalling OS X before - I've got Time Machine and I'm not sure if restoring all my files and applications with that would just restore the OS, problems and all?

 

[blackburn]

You can reinstall it and before restoring from the time machine backup try to see if the issue persists, if it persists it's most likely not an os x problem, but have you tried linux or windows?

edit: the 10.6.3 update has been released try it, and good luck

 

[dougbiznatch]

The exact same thing happened to me. I was watching some torture / rape porn before I turned my speakers down and looked at some giant penises. I forgot all about the porno. So when I turned my speakers up I heard a strange gurgle so I packed my iMac up and took it straight to apple. When I got there, the apple employee busted a nut on my face and told be to get out because I was "embarrassing myself."