AC Line Vibration
 

Not too long ago, I'd say about 50 miles ago at the most, I noticed a vibration sound coming from the engine bay of my car. I checked it out today and its the AC line vibrating against something, but I can't tell what. If i hold it with my hand and pull firmly against it the vibration stops, but once I let it go the vibration starts up again. It only occurs between 2000 and 2200 rpms. Its the line on the right side of the compressor, could it maybe just be the O-Ring or something?