This may not help, but it is a suggestion to check out, because this experience happened to me with a brand new Mustang once. My vehicle's radio quit working properly and started acting funny a couple of weeks after purchasing. It was brand new and under full warranty. I took it to the dealership, who kept my car for almost a week. After calling about my car a couple of times, they finally said it was fixed, come get it. When I arrived at the dealership to pick up my car I asked the service manager what problem they found and what work did they perform. He told me they replaced with a brand new radio.
I wasn't real happy about waiting several days for them to pop in a new radio in a brand new car I had just purchased from their dealership, but without much fuss, I drove away, happy to have my new Mustang back. Well, I didn't get 2 miles from the dealership and the same thing happened with the radio again. I was pissed. I made a U-turn and drove it right back into the service garage.
The service manager looked uneasy as I approached. He could tell I was mad. I told him the same thing just happened, I thought you replaced the radio. He said they did, but if I would leave the car, they would look at it the next day. I said no and demanded satisfaction at that moment. Turned out, they didn't replace the radio at all. Then they tried to claim they repaired it.
Well I made such a spectacle of myself in that dealership, determined to run off customers, the GM finally usher me into his office, while they immediately replaced the defective radio with a brand new one.

The moral is, you should be absolutely sure the dealer replaced the radio the first time. This happened to me one other time with a dealer on a new conversion van with a defective TV. These folks are as unscrupulous as they come. Don't believe they replaced anything, unless they can show you the one they took out of your car. They just don't throw the old electronics away.