U2724DE, M3T107, MacBook Air, headphone audio stops working

The online U2724DE User's Guide page 16 specifies that the #11 Audio Line-out port does not support headphone usage. The port was tested/validated for powered external speakers =

"Since upgrading the firmware to version M3T107"

I do not see firmware M3T107 on the U2724DE Drivers & Downloads page. When I change "Operating system" to Apple Mac OS, I see M3T105. Where did you find M3T107?

Sorry, I meant the audio line-out port of course. I have it connected to powered speakers, and it has been working, until I encountered the issue described above after upgrading the monitor firmware last week.

I installed M3T107 from the Dell Display Peripheral Manager.

So your headphone discussion was headphones plugged into the powered external speakers?

When both are off for hours, assuming that you first turn the monitor on, then the MacBook?

I am not using headphones. I have powered speakers connected to the audio line-out port.

I use a power switch which turns the power on for both at the same, and then I wake up the MacBook by pressing a key on the keyboard.

"I use a power switch which turns the power on for both at the same"

Test without the power switch. Turn both MacBook and U2724DE off. Plug the MacBook power adapter and U2724DE power cable directly into the wall socket. Then turn the U2724DE on, then turn the MacBook on. Retest audio.

Actually the power switch controls the monitor and the speakers. The Mac is powered by Thunderbolt from the monitor.

This issue appeared after I upgraded the monitor firmware. I didn't change anything else.

I am just trying to give you troubleshooting to get around the issue. Removing the power switch is one such workaround.

According to DDPM, M3T107 firmware is the latest. Getting an exchange will not help. At this point, all you can do is periodically check the U2724DE drivers page to see if a newer firmware is released to test. Also DDPM might in future prompt you to install a newer firmware.

My goal with reporting this bug, is to make the maintainers of the firmware aware of the bug. Can you please make sure that my report reaches them? Thanks!

The displays team could not duplicate this issue.
- Which version of MacBook Air (OS version) is used?
- What specific type of speakers are used?

macOS 26.5.1, Yamaha HS5 with a Yamaha HS8S subwoofer.

The displays team was not able to duplicate the issue with following hardware =
Macbook M4 Pro, macOS 26.6
Macbook Air M2, macOS 26.6
U2724DE loaded with M3T105 or M3T107
Dell AX210 3.5mm + USB speaker
Third party 3.5mm + self-powered speaker

They did not have Yamaha HS5+HS8S.

They suggest that you update to macOS 26.6 and retest.

In macOS 26.5.1, Apple introduced aggressive energy conservation profiles aimed directly at standard Apple Silicon (M-series base tier) to prolong sleep-state battery life. When waking from deep sleep, the graphics driver in macOS 26.5.1 fails to reset the audio clock timestamps inside the DisplayPort blanking intervals. The U2724DE monitor receives the video frames, but its internal audio processor sees an invalid or missing clock signal. The monitor's DAC assumes the audio stream is dead or corrupted and puts the physical 3.5mm line-out jack into a muted, ungrounded state.

When customer run the monitor's self-diagnostic test, it forces the monitor to reset, dropping its Hot Plug Detect (HPD) voltage line to zero. This physical drop forces the macOS 26.5.1 graphics driver to completely crash and reload its display layout. When the driver reloads, it performs a full, fresh hardware discovery sweep. It rebuilds the DP Alt Mode architecture from scratch, correctly injects the missing audio packets back into the video stream.

In the macOS 26.6 update, Apple adjusted the timing sequences for standard M-series chips. macOS 26.6 forces the graphics driver to delay its hardware check until the Thunderbolt bus has completely stabilized, ensuring the DP Alt Mode audio stream and its clock packets are successfully established every single time the laptop lid opens.