Since you noticed the sound drops specifically when RAM usage spikes around 3.2 GB and clears when hitting device optimize, this strongly points to background process throttling and Android Audio Focus conflicts.On older One UI builds on the Note 9, ...
Had this exact same problem on my Note after the recent update. Snapchat actually changed the default behavior for the Friend Solar System (Planets) feature due to privacy concerns - it is now turned off by default even if you have an active Snapchat...
