I have same issue, thank god for the heated seats. I have leak from flange.

As soon as it gets warmer I will replace flange and bleed the system hopefully this should solve the problem.

If you have no leak try bleeding first very simple (www.audidiy.com) and see if that solves the problem.

Good luck!!

 

+1
There's a procedure for draining and refilling coolant to get rid of any air pockets. I opted to just pay Audi to do it, lol.

 

Just idle the car with the coolant cap off and let it get hot. Once it heats up, the air will bubble out and you will likely have to add coolant.