i now know that audi uses a 'diversity' antenna system - there are 2 plugs on the back of the original unit and apparently one goes to the front of the car and one goes to the back...so i'm researching where to go from here.

It might possibly be related to that, not sure.

When you said "didn't work", I thought you meant it really flat out didn't work. The fact that you hear static means the tuner is working but there's something wrong with the antenna connection. It might be something as simple as a frayed antenna wire, intermittent at best, and would tend to start and stop functioning as you changed the angles and stresses on the connector.