Thread Modes Some Help with Audio in a car

So I have a question about the sound, power supply, because while everything is turned on (car, Raspberry, Audio Amps)

My Py is feed as follow 

I have + and Ground from the Battery, this is connected to a 12v to 5v 10A Converter, Before the powerleads go directly in the pi it has a Capicator before to stabilize the current.

I use a Hifiberry as sound, but the problem I try to discribe hasn't do anything with this card cause it's with every audio card i use.

So when i turn the key of the car power goes to the converter.. i turn a switch and the pi turns on. Everything is ok!

But when I shutdown the Raspberry and the switch of i get a blurp every once a second on my speakers.. 
It only appears when the circuit is broken... and so a ground loop is caused... 

How can I resolve this... for example if i want to take a quick drive i don't need audio nor raspberry pi to be turned on... but if i don't i get that annoying blurp al the time.


Could this be solved by grounding the hifiberry seperatly to the car true the 5v connector aside R14


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