If I start my car when it is cold I get an exhaust rumble coming from under the hood but it goes away after less than one minute and the car has to cool down for several hours before the exhaust noise comes back. I brought it into the local shop (German Motor Works) and they were not able to find the leak, they recommend that I bring it to the local dealer. Has anyone had a similar problem and what fixed it?

 

Wait for your car to be cool and start up the car and just run your hands over the exh system. Best places to look are at the turbo to manifold and around the flex section of the dp. The gasket and flex section both have known to cause issues.

 

It is likely your secondary air injection system. This is normal. It basically opens up the exhaust and pumps it into the air intake to recirculate exhaust gas during a cold start. You should be able to hear the noise coming from the air filter. There is a black hose on the passenger side of the air box, remove it and plug it with your finger and the noise stops. Personally I hate the noise, but haven't invested any time in removing the system.