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The reason there is whine on aux and AM is that there is multiple grounds and or poor grounds. If one was to take a multimeter and measure the resistance of the grounds of the radio to the battery and the resistance of the grounds to the XM I am sure they are different. Ultimately we want 0 ohms resistance between the radio, XM receiver and the negative post of the battery. I am not talking metal chassis ground but rather negative post of the battery. At the same time if we measure the resistance of the negative post of the battery and the chassis of the vehicle and it is anything but 0 ohms resistance the ground from the battery to chassis must be improved. If the negative battery cable has any green stuff coating the copper wire inside the ground cable it increases resistance and hence all these problems result. All noise problems can be traced to these principles. In short make sure the radio ground and the XM ground have the same 0 resistance to the negative battery post.
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