99 intrepid 3.2 wireing issue

I have an issue with certain things in my car when my car is started or in the on position my stereo volume goes up and down by its self and my lights in the shifter go out and back on and also when I turn the volume down on my radio I hear like a static noise
but when I turn the key to the accessory position all is fine light stays on and radio go to normal volume and stays btw its a factory radio never been removed what could cause this problem