sound output device keeps changing itself constantly

You may be on to something there ! I didn't think of it but surely dirt can be conductive enough to trigger spurious
indications about a headphone inserted or similar. I will try cleaning my headphone jack.

My iMac does the same. I have never had anything connected to the external jack. It is nothing to do with the jack switch. It cuts in and out at random. The preferences switches from showing the only output as "Internal Speakers" to showing the only output as "Digital Out". When I try to change the volume it shows the volume popover with a 0 with a diagonal bar to indicate there are no volume controls.

Today there was no sound for about an hour when I got up, then it just started to play then after 10 mins it cut out again. Since then it has cut in and out several times. Tried PRAM reset and all that stuff. No help. Problem is getting worse. Now I can't do any chats (iChat, Skype, etc) from my imac which means I may have to move off of it for work all together.

Come on Apple, this is a real problem and I'm guessing it is a software issue.

I found that time machine backups do this. Whenever a time machine backup is running in the background your audio output switches back to whatever the hardware default is the OS X device (built in speakers generally). Wait a few seconds (up to 1 minute) for this to pass and audio switches back to what it was on. Alternatively just don't let time machine backups run on a schedule and switch them to manual (it will still happen on manual launch though). Hope this helps.

I am having a similar problem. It started after I paired a bluetooth headset for use with skype calls. Now, lion will periodically, without prompting or warning, switch the output and input audio device to the bluetooth headset and I will no longer hear any audio from my iMac speakers. And since my bluetooth headset is not always connected, I get the added insult of being interrupted by a an error dialog stating

A Bluetooth audio error occurred.

There was an error connecting to your audio device. Make sure it is turned on and in range. The audio portion of the program you were using may have to be restarted.

Stop using headset

In this case, it shouldn't have anything to do with the physical headphones jack as I do not use it at all. Apple, as this is happening many times a day, I'd really appreciate an acknowledgment of the issue and a fix.

I found that this auto switching of sound output options is why i am seeing a skip in audio. I created a thread here with all the details. (https://discussions.apple.com/thread/5960319)

Anyone figured a solution for this out yet ?

Apple doesn’t routinely monitor the discussions. These are mostly user to user discussions.

Send Apple feedback. They won't answer, but at least will know there is a problem or a suggestion for improvement. If enough people send feedback, it may get the problem/suggested change solved sooner.

Feedback

I have exactly the same issue. Both iMac and MacMini started showing these problems few weeks back. About 6 months ago I had this same issue and took the iMac to AppleCare.. one cable was replaced but it didn't help. Just as I was about to send the iMac back it suddenly started to work.

Update on the situation,

I got the problem fixed (at least for now) by using toothpick to clean/scrape the socket walls. It is a bit weird that it worked since I have used speakers since day one so there can't be any dust there.

This JUST happened to me (sound output swithing from speakers to headphones and then back and forth) while watching a You Tube video, at the same time my iPod popped up telling me I had recently purchased songs from iTunes and I could set it up to sync.

The iPod wasn't connected to my iMac, so I opened the Bluetooth control panel, and it was paired with my iPod which I hadn't done. I use a wired keyboard and mouse so I just shut Bluetooth down. Twenty minutes on now and no issues.

This is on a late 2009 27" iMac running a fresh CLEAN install of Lion pathced to 10.7.1 and an iPod touch that I just updated maybe 2 days ago. I'll update this post if it flakes out again.

I'd agree id has nothing to do with the headphone jacks in both our cases. I've plugged headphones into this machine maybe once in 2 years (and not recently).

Since my reply last week and shutting off bluetooth I have not had a single incident, so I'm fairly sure that's the cause for me.

Hey guys,

i think i've found the cause to our troubles.

Today, i finally went to the apple store, and after checking it, the lady said that it is due to a faulty logic board (moterboard). It is a hardware issue and not a software issue. So, if your com automatically switches from internal speakers to headphones and digital out for no reason at all, you should really go to the shop to have your com checked out.

Tim.