Radio/tape Cd Player problems of the 2009 Toyota Scion Tc

I bought my car brand new in December 2008 and within a week I noticed that the radio did not get good reception in some areas. I brought my car into the dealership where I purchased the vehicle and they could not duplicate the problem. I have this problem occur on a daily basis and the slightest things cause signal interruptions. Some of these items are other vehicles, metal building overhangs, telephone poles, rain clouds, fog, trees, and random other items. I have had my car in the dealership 5 times now and they have replaced both the radio and the antenna that connects from the radio to the external antenna on the rear deck lid of my car. Neither one of these repairs have fixed my vehicle. The dealership has noted on 2 of my repair orders that they have driven other cars on the lot like mine and have experienced similar issues.