sat nav guidance volume help driving me mad

[SM8]

hi guys....i normally play files from my sd card and my sat nav voice guidance and speed camera bleeps and notices plays loud during the music.....i havent got it on the attenuate setting where the music fades down.....this way i can keep listening to the music and hear the bleeps for the speed camera and hear the insturctions for the nav

 

BUT

 

i have recently burned an audio cd for my car and when playing the volume of the guidance is barely noticeable and i can hardly hear it at all ....whereas as soon as i put the same song on from the sd card.....the volume for speed camera and nav is back to normal

 

any idea whats going on as i would rather listen to music from my cd as oppose to the sd card due to start up time and lag from sd card......

 

please tell me theres a solution ive tried everything i dont understand why this is happening !!

 

i have an avic f900bt btw