I set my audio settings to a custom value, generally just lower than default. Every time I enter a new zone the sound comes back. The values in the audio settings are displayed the same, and once I adjust any of them a single notch the audio returns to the custom setting.

This basically just forces me to reopen the audio settings every new zone, which is a bit annoying.

Happens to me too, especially noticeable when entering Hunter's Dream

It seems to only affect the Overall slider so a temporary solution you could try is leaving it alone and adjusting the other sliders.

Which slider are you adjusting?