Audio ducking

I use my phone daily for podcasts/music and have never had this issue before a few weeks ago. The audio regularly lowers in volume for c.10sec as if for an alert.

• happens in multiple apps (Eg. pocketcasts, Spotify, YouTube)
• happens whether playing back via phone or any different Bluetooth device
• voiceover is off
• almost always have phone on silent
• ducking still occurs when on do-not-disturb mode
• when it happens it is not tied in with any visible notification or banner pop-up
• have tried hard reset and reinstalling pocketcasts (before I realised it was other apps too)

I cannot recall changing any notification settings, it just suddenly started happening and it’s driving me a bit mad I can’t deduce the issue!