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I have the same problem. I just soldered the car charger to the amplifier power input and connected the bluetooth module using the audio jack in the back. It works, but the background noise is terrible. Also, the noise seems to increase if I touch the cables, as if I was acting as a kind of antenna. If the volume is low in the amp and set to 100% in the computer, the noise can't barely be noticed. But as soon as you turn up the volume knob.. it's pretty annoying. Would around loop isolator work here? What about using a separate power supply for the usb bluetooth receiver?