How to fix the pumpkin head unit frequency noise or hissing sound?

Due to the car differences, some special car which have more metal electronic parts would have some static/frequency noise when they install our head unit, so how to fix it?

About the noise, when the current flows caused the voltage instability, it will lead to some frequency noise. You need to install this filter so that the EMI can be shielded.

Just need to cut off the “B+” wire and connect like below,and the black line from the filter needs to joint the GND line from the ISO cables.