Noisy rattling noise on idle and ticking noise after shut off. Audi A6.

In sunny Los Angeles. I am now 1 year into my 3-year lease at 6500 miles (I don't drive much). I'm rocking a Audi A6 Quattro 2.0 premium and a noisy phenomenon is still dogging me. I began taking it back to the dealer almost immediately (probably five or six times over the course of the initial months). It has a rattle during idle or low speeds - most notable in enclosed spaces, like parking garages. I have had two loud backfires. And the ticking or clicking is so loud after shut off I can hear it from my garage all the way to the side walk - about 50 yards. At first they told me it was the catalytic converter cooling down - but this is really loud and is NOT noticeable on test drive. Only after my commute to work or home does it do this. After the second backfire, they ordered a part from Germany called a resonator, because there was a noticeable rattle coming from underneath the car at regular intervals - like ever 10 seconds. In service this past January (6 months into the lease) they replaced the exhaust because it was clogged due to it being "faulty"
Also, the city MPG is abominable - 13 to 14 MPG. The only time I get near 20 MPG is on the freeway. I drive it in the COMFORT mode.
The other issue is the groaning brakes, also from the start, which other members have also noted on their cars.
Has anyone else experienced these combustion or combination of noise issues right from the gate?