Created attachment 288727 [details] dmesg On hard boots a clattering sound can be heard from the speakers as X starts up on my laptop with hybrid Intel/AMD graphics on kernels from 5.5.18 on. An audio
Created attachment 288729 [details] audio An audio file of the sound is attached (I hope), as is a dmesg output. Other PCLinuxOS users have also complained of this problem on these kernels. Some report they can silence the sound by muting the speakers and others say they can't. See https://www.pclinuxos.com/forum/index.php/topic,152310.0.html. I do not know whether the distro is significant. However, I have tested with mainline kernels to eliminate distro-specific kernel patches. 5.5.18 is also the version which fixes bug 205291 so I suspect the two issues are related. A look at the changelog suggests commits d0c160b21c42860833d270ca161d66e5adc1ceab, a4b7ec793b4b83dc76aba41192b1527942ee469d, and 13b267c8d7921b8b6721dd0d928aeccff49136cf as possible suspects, though that's just a guess on my part as they mention sound and mux. Steps to reproduce using an Acer 5810TG laptop (if you just happen to have one to hand): Install kernel 5.5.18-5.6.6 and shut down, boot from cold. Usually this will produce the effect. Other hardware produces similar results, but I couldn't determine what the other affected people were using. If I get that info I'll report it here.
The problem is also present in kernel 5.4.34 now, so it's evidently been backported.
All three of those commits were added in 5.4.33!
Other models on which this problem has been reported: HP Zbook 15, CPU Intel i7-4900MQ, Nvidia Quadro K2100M (2Go), 16 GB Ram HP ProBook ThinkPad X230. Hope that helps.
The bug is only present on my laptop when running on battery and vgaswitcheroo/switch shows DynOff for the radeon GPU. However it is gone altogether in version 5.6.11, but bug 205291 is back! Seems it is related to the selection of DynOff. Is something happening repeatedly which should only happen once? Not convinced this should be closed, but reopening bug 205291 as that problem is back.