Q: Sound stuttering after Mountain Lion install

I have too say that my user experience was almost exactly like yours, till the point it became unbootable and I checked my HDD with a working tool, not Apple useless disk utility.

Snow Leopard: Never had a problem.

Lion: Some slowness and spinning wheels.

Mountain Lion: Serious slowness and Media stuttering (never experienced before)

Didn't get the same behavior with other OS in the same disk.

Reinstall didn't solve.

Got it to become unbootable, really, even other OS refused to boot.

Start analisys through a linux live session, HDD readable, but full of bad blocks (Apple disk utility never warned about that, it only suggested repair, which completed successfully. It's kind of useless).

It got me a long time to go and CHECK THE HDD WITH THE RIGHT TOOL. *My case* was the HDD, still, it was usable, it was just ML that dealt really poorly with bad blocks compared to the other/previous OS, so it helped me think it was only ML to blame. Conventional apple diagnostic tool also helped for that.

As I underline, it was just my case.

Pepper, you just proved my point.  It said you needed a new drive and apple diagnostics advised replacement.  That sounds like its detecting bad blocks.  If you need it spelled out then that's your own issue to decipher.  Apple writes software for English speaking not technical people.  If you are a computer person as many of us are, you learn to speak both languages with apple.  I think you're the only one with a faulty drive. 

In another suggestion, I read a suggestion this issue might also have a tie in with AirPlay.  Since most of the affected computers have airplay capability, it has been suggested that the computer is getting confused between what it should display and the airplay feature.  Even when the feature isn't being used.  This could be a worthless guess, but it never hurts to throw it out there. 

It never said I needed a new drive. I don't even remember what it pointed, and worse, after such repair (operating as a windows chkdisk routine after some brute shutdown, does that means hardware replacement?), it said: repair successful.

It just looks like a common filesystem repair routine. It's not my issue for sure, it's plain bad diagnostics.

I can't stress enough, I changed my drive, wasted my money with this, and had gone several times to the Apple Disk Tools. It never helped providing useful information.

Your said your drive had bad blocks, now it was repaired?  I'm so lost in your story.  You need to clarify as it doesn't make much sense.

Easy, I've found out it had bad blocks only after starting a linux live section, starting its disk utility and then, at last, looking at useful diagnostics information.

Before that I was just wasting my time with useless apple disk utility saying some filesystem repair was needed, and it was done, and it was successful...

Going back to your Origional point of slowness and it progressively worse, no one else has had these issues. My system speed is the same. I just can't make it do media as it should.  Everything else works. 

Wrong, go back to page 5 and see the "New Theory", it's not only my point. You assert a lot without checking the original reports.

This isn't the only thread I read.

I'd like also to point out that, once upgraded to Mountain Lion, my system was slow before indexing, pram resets and stuff. After that my system acquired a normal speed, with ocasional mouse/typing lag, but the really most outstanding issue was the sound stuttering. I was using the system almost normally, I just could not play any song in iTunes. This looked very weird.

As time passed by too much, the lags aggravated, and Apple Disk Utility didn't helped.

Stuttering showed up in ML only. In Lion I had only some slowness, but it could play music.

Are you still talking about the 27" iMac 2011, pepper_chico? The problem is caused by software, not by hardware…

What? I didn't know this was a thread about 27" iMacs from 2011. I'm talking about the issue.

People that persists this thread is about iMacs solely should move to another thread or create one. We alrealdy know how to read in which section this thread is, which OS it's talking about and which issue. It's not stated anywhere that this thread is to deal with specfic models solely.

ok, then you know it now 

I said some similar several times already, your commentary is a little weird, since I own a macbook pro.