Hello, I am having trouble with my XM Sattelite radio reception. I can only get a good signal when driving north (back of sharkfin antenna pointed south) or driving west (back of sharkfin antenna pointed east). Otherwise, the radio says 'aquiring signal' or signal goes in and out. Wondering if this would be a bad antenna or something in the radio itself. This is on a 2013 Optima LX without navigation.