ZForce1

I know there have been vibration questions in the past, and I have tried to read as many of them as I could find. I have a '99 Z28 A4 with 107xxx miles, of which I am the original owner. The car has always had a vibration at idle at times, but I have always lived with it since it seems to be an inherent problem with our cars. I am tired of living with it, and lately it seems to have gotten more noticeable. I recently put a poly trans mount on, which transmits more vibration, and I am going to put a stock rubber one back on. Has anyone ever effectively nailed down what causes this vibration? It is most noticeable at a stoplight in gear. Put it in neutral and it is not noticeable, I would expect because the vibration is not carried the rest of the way down the driveline as much. It is intermittent, though. Sometimes it will idle perfectly smooth in gear at a stop, other times the car will shake. I can't think of anything that would play games like that.