My 2018 automatic car with a turbo is losing engine oil. I've checked with the service center; there's no blue or white smoke from the exhaust, and there's no sign of oil leakage on the engine exterior. Both the oxygen sensor and spark plugs are clean. The service center couldn't find the problem. Anyone knows what might be wrong?

After warming up my 2015 S5 1.5T, the transmission makes a "dang dang dang" noise when I give or release the throttle. Not sure what's wrong. They say it can't be fixed. Has anyone replaced the transmission? How does it feel to drive after the replacement?