Make the symptom reproducible
Play the same short audio clip before and during a call. Keep the volume fixed and note whether the change affects channel separation, tone, interruptions or delay. Those are different observations and deserve different tests.
Check the audio input and output inside the app, not only the operating-system default. Games, meeting apps and browsers can remember their own device selection.
Test the microphone branch
If the headset is using Classic audio, its microphone can change the playback path. Try an available built-in or USB microphone as a controlled comparison. Close the call first, select the alternative input, then reopen the call.
If the sound still changes, close other communication apps and repeat. A background application can keep an input open even when the app you are watching appears idle.
Keep a short before-and-after record
Write down the app, selected devices and audio transport for each test. Record whether the change happens in another app with the same devices. This separates an app-routing problem from a system-wide pattern and makes a support request much more actionable.
- Same playback material and volume
- One changed setting per test
- Actual app input and output names
- A final recording or call test before important use