Probably your fan is just busted and is contacting the plastic shrouding. had the same problem on my 4th gen. It sounds somethin like sticking a piece of plastic or paper into a ceiling fan right? Have you actually taken the fans out and inspected them? Be careful of the A/C line next to the fans, try not to bend it too far. Go to a junk yard and find one that's an original fit for your car. I got an aftermarket fan from advance and I had to do major ghetto rigging (drilling bigger holes and all that) to mount it in the shrouding.