Volume fluctuations (not caused by notifications) on OnePlus6

[Haz88]

ISSUE

After the latest update, I have had an issue when playing music in my car by Bluetooth where the volume will seem to fluctuate dependant on the music being played.  It's like an adaptive EQ as it will play the music normally for two seconds as it fades down.  

I've seen similar problems for computers but not for phones and cannot for the life of me find a solution and it is destroying the listening experience as it completely kills the songs. 

I've tried

- turning the normalisation off and on and restarting the app. 

- uninstalling and reinstalling the app

- messing about with options on my car 

- messing about with options on my one plus 6 (looking for possible adaptive sound/soundalive options that could be interfering with it) 

- searching the OnePlus site 

But have had no solutions. Someone please help as this is really doing my nut in, as if the traffic wasn't enough to do that! 

Plan

Premium

Country

 Uk

Device

OnePlus6

Operating System

OxygenOS 9.0.2