very little slack, I would pull out the radio and make sure it is secured. Other than that I would start testing all of the harness pins on the back of the radio to make sure you are getting voltage through them. I believe it is marked K in the diagram on the radio. Also there might be a fuse on the back of the radio that may be the culprit. Try the audio forum, I'm sure someone has had this problem. They are slow to respond so be patient.
2005.5 Audi S4 4.2L 6MT Quattro Black/Black
19" DPE R16 Liquid Cinder Forged | Premium/Winter Package | RS4 Grill | NAV | Carbon Fibre