linux – What could be causing static on HDMI Audio with Pulseaudio

Using Yocto Hardknott release, I am running Pulseaudio version 14.2 on the kernel version 5.10.72.

I use the module-combine-sink to stream audio to both Lineout and HDMI simultaneously.

About 50% of the time, I hear static on HDMI audio exclusively. Lineout is static free.

I render audio to Pulseaudio mainly through gstreamer pipelines using the pulsesink element which outputs audio to the Pulseaudio server. I also utilize the pa_simple_write from the Pulseaudio API to write audio buffers.

I have confirmed that timer based scheduling is disabled with module-udev-detect tsched=0

The audio being streamed is at 48K sample rate and both default-sample-rate and alternate-sample-rate are configured to 48K to eliminate possible resampling errors.

I’ve checked top to confirm that the CPU isn’t under duress when the audio is static-filled.
I’ve enabled Pulseaudio verbosity with the -vvvvv flag on startup, but no underrun errors are logged when audio is static-filled.

I would appreciate more thoughts on how to further investigate and resolve this issue.