Civicnation2014

I have been using Amazon downloaded MP3s ever since I bought my car in 2008. I have the Sansa card reader and use 2 Gig SD cards. But in the last few months when I have bought an MP3 file from Amazon and downloaded it, there has been a good chance that the file would not play on my car system. I haven't contacted Amazon yet because I can't see that there has been any change in the format of their files. They are all mp3 files. Itunes files won't play which I found out early on. Amazon was great because their files would play in Itunes and just about anywhere. Now they don't. Anyone else notice this change and have a possible solution?