whilst i was in the dealers today getting my car sorted, i mentioned to the tech that i had had to restart the car the other day as there was a low hum coming from the speakers, and the sound from the system sounded crap. turned off engine , could still hear the hum, wasn't until the car fully shut down that the hum stopped. restarted car hum was gone.
Well apparently this is a known fault and Audi are working on a software upgrade to fix it. so you don't have to restart car every time you get the fault you can just reset the stereo by pressing Menu, the round MMI wheel, and the top right hot key!! that resets it.
they told me as soon as a software fix is out i will be notified. everybody else that's not getting the fault will just get the update next time there car is in for anything.!