iMac 2017 audio cutting off over line out

[Icestyle]

So while I'm very satisfied with my new iMac there is one extremely annoying issue:
After some time iTunes (VLC too) playback starts stuttering (i.e. sound is cut off for a few milliseconds). This can happen once in a few songs or as often as every second. When I unplug my speakers and plug them back in, the issue gets less worse but persists and comes back in the same intensity as before after some time. Same goes for restarting the iMac.

This only occurs over line out (and headphones, so the speakers can be ruled out).
When I use a Bluetooth receiver connected to the same speakers, everything is fine.
When I use the internal speakers, everything is fine.
When I use the audio out on my external screen over DisplayPort, everything is fine.

System Console does not show anything out of the ordinary.

The options I see here are:
(a) There is an issue with the audio driver on the new iMacs
(b) There is an issue with this specific installation of macOS
(c) My logicboard is damaged

(a) seems unlikely as I couldn't find any thread about this issue
(b) is somewhat unlikely although I could try to reinstall macOS
(c) this would be the third iMac in a row with issues. my 2009 iMac was DOA, my 2011 iMac had a failed power supply and now this.

For now I will just use the bluetooth receiver...

 

[ApfelKuchen]

There are lots more possible causes for this issue than the three you listed. Rather than try to self-diagnose, why not have Apple look into it?

The headphone jack is normally on the I/O Board, not the Main Logic Board. The conversion of digital to analog happens outside of the operating system, in hardware, so if the issue is not common to all audio outputs, likely it is not due to its common, digital source within the OS.

 

[Icestyle]

Of course there are other possible causes but I don't see how calling Apple could resolve this issue.
I don't think there is a separate I/O Board in the 5K iMacs.

 

[ApfelKuchen]

You're right, there isn't a separate I/O board - I'm too used to looking at MacBook tear-downs.

Why call the manufacturer while your product is covered by warranty?? It sounds like a product defect to me, whatever its cause. When it's under warranty you don't have to diagnose or isolate the cause, you just have to tell them, "It's broke." It's their job to figure out why it's broken and to honor the warranty. Take advantage of that while you can. After a year and a day it'll still annoy you, but you'll also have to pay for the parts and labor.

If you distrust the skills of the people at Apple, and don't want to risk spending your time pursuing a warranty repair... there's likely not much I can say to change that. I have an aunt who has been hobbling around in great pain for many years because she doesn't trust doctors. Nobody's been able to persuade her to have her problem fixed. She's finally ready to have it done, because she can now see that her independent lifestyle will end soon if she doesn't.

Speaking as someone who, over his 62 years, has usually been the guy to fix things when they're broken... I appreciate getting good information from the people who come to me with their problems - "When I do this, it works fine, when I do that, it doesn't." However, when someone hands me a diagnosis, with little or no evidence or specific knowledge to back it up, it just gets in the way of doing my job. "Needs a new motor." "Really? What if the motor is just unplugged, or the belt is broken, or the motor control relay is fried?" If I reject their hypothesis out of hand, it just leads to bad feelings. If I take time to test (and usually disprove) the hypothesis, then gently explain why the "patient" was mistaken... it's a waste of everyone's time.

 

[Icestyle]

I should have mentioned that I need the computer now. If the issue persists after updating or upgrading macOS or reinstalling the system then I will have them fix it.