Audio over Hdmi issues, Ubuntu, RTX 3060

I came across weird issues with sound over hdmi Ubuntu 2404. I am generally not familiar with linux, so if I should perform specific tasks, pleas describe detailed.

My Setup

Asus Prime Z590-P
ASUS GeForce Dual RTX 3060 12GB V2
Intel Core i9-11900KF
One Screen connected to DisplayPort 1 in 2560 x 1440
One Screen connected to DisplayPort 2 in 1920 x 1080
AV Receiver connected to HDMI

Issue #1

  • Install Ubuntu 2404 from ISO
  • Install Cuda following instructions at cuda download site, thereby installing driver 555
  • restart

Result: there is no sound over HDMI, there is no audio signal at the receiver
But I can even see the vu meter moving as sound should play
Audio is fine with noveau drivers

My diagnose:

In Settings / Displays the resolution of the HDMI device is by default 3840 x 2160
I set resolution to 1920 x 1080 and 60 Hz sound will immediately appear, but see below

Issue #2

Do as above, but use any driver between 535 and 555
Play any sound, for example in Firefox load https://www.youtube.com/watch?v=nMfPqeZjc2c
→ notice audio drops out repeatedly and frequently when you do normal work like opening windows, switching between applications, opening files…
Audio is fine with noveau drivers

My diagnose:

In Bios the PCIE Generation setting for the graphics card MUST be set to Gen2
Gen3 or Gen4 or Auto will produce drop outs
Bios version was 1803 as well as latest version 2002
Upon real close inspection I believe this issue also affects Windows 11 as I do notice rare and tiny audio distortions there as well, there also using latest driver 555

I hope you can reproduce the issues, I can turn both issues on and off 100% by changing the described settings

Greets, Rainer