Sound/Video Problems on iMAC?

[gdubb85]

My wife has a 27" iMac with Retina 5K Display (Late 2015), 3.2GHZ i5 1TB Fusion 8Gb Ram and it has a few issues that I am trying to diagnose..

Several months ago it start to to very seldomly on shutdown show a quick flicker of rainbow colors before the screen went black to turn off. We shrugged it off, because the display was fine at all other times.
Last night the sound would not work at all on Chrome (Youtube videos, music, etc), VLC player or WinAmp player. It worked fine and sounded normal quality on Firefox, Safari, iTunes, Quicktime. I fought with it for hours, resetting PRAM/SMC, uninstalling Flash player/reinstalling... It did not matter if headphones were connected, internal speakers were used, or Bluetooth - sound either did not work at all or worked fine.
This morning, all of the above applications that did not work at all suddenly worked with sound, but the sound was weak/tinny/low volume and just didn't sound good even if Bluetooth headphones were used. Also, image thumbnails flickered in Chrome on a site she visits but were fine on the other browsers.

Anyone have any clue as to what might be going on and what else to do to diagnose it? Her display has had no problems other than the above things mentioned, I just included it for completeness and because of the image flickering issue in Chrome - the main issue is sound. The behavior changes without changing software at all which makes me think it's hardware, but certain applications are not affected at all which makes me think its software... so utterly confused...

 

[Lunder89]

Given what you have already tried, I can only think of two more things to do.
The first you could try, is to create a new user on the Mac, and then try using that for a couple of days. If it works fine, some configuration file somewhere might be causing the problem.

If it changes nothing, the only real thing to try, would be to reinstall the Mac.

Since it could be a sound driver causing the problem, trying to install macOS again, (without deleting the harddrive), could solve it. But since you need to make a backup of everything before trying that, you might as well delete the harddrive, and just set the Mac up, as if it was new. That way you eliminate the chance of some random configuration file somewhere is causing this.

You can find some help on how to reinstall the Mac here: https://support.apple.com/en-us/HT204904

 

[gdubb85]

Given what you have already tried, I can only think of two more things to do.
The first you could try, is to create a new user on the Mac, and then try using that for a couple of days. If it works fine, some configuration file somewhere might be causing the problem.

If it changes nothing, the only real thing to try, would be to reinstall the Mac.

Since it could be a sound driver causing the problem, trying to install macOS again, (without deleting the harddrive), could solve it. But since you need to make a backup of everything before trying that, you might as well delete the harddrive, and just set the Mac up, as if it was new. That way you eliminate the chance of some random configuration file somewhere is causing this.

You can find some help on how to reinstall the Mac here: https://support.apple.com/en-us/HT204904

Wow creating a new user solved the issue! My wife is either going to just start using the new profile and move any files over or we'll reinstall to get a fresh start... I don't understand how things just change sometimes... (how can an audio setting change without the user making changes?!)

 

[Lunder89]

If only I knew . A few months ago all my video files were suddenly mistaken for audio files. The same trick worked then.

 

[BrianBaughn]

How does this happen? Improper shutdown or disk ejection, third-party software, monkeying around with system files, voodoo.