Iphone Proximity Sensor Broken?

Hey guys, so 2 weekends ago I replaced my shattered iphone screen with one I bought from Amazon for $30. Everything overall is OK. The screen is not the same, though. Sometimes the screen kind of shakes and is frazzled, if that makes sense, especially in the corners and around the edges. The biggest problem however is I believe the proximity sensor might be broken. Whenever I'm on the phone with someone, the screen does not go black like it usually does, and as a result my ear or cheek or whatever press random buttons like Mute, Add Call, etc. that mess up my conversation. It is annoying as hell.

What do you guys suggest I do? It would be a pain the a** to go inside the phone and try and fix the proximity sensor. I have AppleCare (Not plus, though). Can I take it to the Genius Bar and try and get it fixed? Will it matter that I replaced the screen myself? Thanks guys.

Tom

don't mean to update this post but i'm having real troubles here! also when i shake the phone i can hear something rattling around in the phone, especially near the top where the sensor is. thing is, this rattling sometimes occurred even before i replaced the screen.