Electrical faults with radio

[JDL]

Hi so this is my first post here, I bought an A3 8P a couple of days ago, and I've discovered a quirk of my car, 

the radio intermittently turns off (black screen) and then upon pushing the mute button turns back on. 
it's weird because there are times it's fine and will stay on continuously throughout my drive, and then there are times where it's every other moment it's off again. 
I can't tell what causes it but from my experience so far the position of the volume dial affects whether it goes off or not, there's a region where it's bad and then a region where it's somewhat better.
Opening the card holder has also caused it to turn off

any ideas as to what the issue is?

thanks