Volume very loud when calling

[MKoers]

Every time I make a call of get a call through my B&M carkit the volume is extremly loud.
I always have to turn it down.

Even when listening to media player it go's up.
Is there a way to change this? As it's pretty frustrating.

If it's important I use a Iphone 4.

 

[Juggers2k]

Have you tried adjusting the aux input volume on the head unit?

 

[MKoers]

Yep, it's been set to 1.
Even tried taht today when the media player was playing.
Volume go's down when adjusting it.
But once I leave the menu it go's up again.