Volume is lowering on songs via car bluetooth

[nickspotify]

Hello

I recently got a car which allows me to do play music via bluetooth and decided to start using spotify to listen to music in the car.

I like to listen to a lot of bass heavy house and I've noticed that the volume during tracks will suddenly go quieter, I don't seem to really have this problem when listening to all genres and I've mainly noticed it when listening to electronic music. Even on full volume it's not that loud and if I turn the radio on then the music is much louder. Often when a new song starts it will begin loud and then go quieter. I've googled this issue and I'm not the only one who's had the problem. I've followed the advice that most people have said in other threads such as disabling auto normalisation, turning the EQ off, closing all other apps but nothing seems to fix the problem.

I'm currently using an iPhone 4s as my 6 broke, if that makes any difference.

Are there any other suggestions which might help to fix this? I bought Spotify premium but I'm considering cancelling it if it continues to cause issues.

Thanks