Downloaded iOS beta, and iphone won't plug into radio USB?

Before, I used to be able to plug my Iphone 4 into the USB slot in my car radio and it would play my music through the car speakers. I recently updated my phone to iOS 7 beta. Now, whenever I plug it in I get a buzzing noise, or nothing at all and the radio sometimes says "no file" instead of giving a song name or saing "iphone- read." (even when it says Iphone-read it sometimes just buzzes."

Before this update, I had absolutely NO problems with this, so i'm convinced that they're related.

It's a BETA and you are only suppose to have it if you are a developer. It's not stable and nowhere near the final version, so expect the worse. In fact, Apple clearly states that they would advise putting the beta on a testing device so that you don't have all of these problems on your personal device.

Well serves you right then, for trying out a developer release which can be buggy and unstable. I once downloaded Goldmaster Mac OS X Mountain Lion and it caused my hardware to fail. My friend's iOS 7 developer preview also crashed his iPhone 5.

So an advice from me, don't try out developer previews unless you're really sure of what you're doing and are prepared to make sacrifices and losses.

Is your device's UDID registered? A lot of people have reported issues with iOS 7 if they try to run it without having their UDID registered on a site like http://www.instantudid.com/.It's $5, and I haven't had any issues at all with my 4S.