Hi I have a A4 B8 2008 S line and for the past year or so I have intermittently been hearing a knocking sound inside the car from the middle area near the fans. It seems to be coming from somewhere inside that area and there is no pattern to when I might hear it. It's fairly loud, sounds a bit like when closing an old school spring loaded glasses case. It doesn't matter if the car is idle or driving. I may hear it one day then I won't hear it again for weeks. My car is regularly serviced by the dealer and also recently had the engine mounts replaced. I did mention this at the time of my last service but nothing was found. Would appreciate any help?