Audi technician used the same technique with me. ie. He got me to listen to another A3 tfs 2.0 except that I pointed out that his had over 20,500 mls on the clock compared to my 2,500 and we did not know the history of his. Getting customers to compare cars seems to be a standard Audi response!! My noise developed at about 2,200 miles. It wasn't there before that. It's probably a pulley or tensioner, not injectors which you will hear anyway. It's there shortly after start up and when warm and very noticeable at tickover. I compared my car with the courtesy car (2.0 tfsi s line) with 3,000 on the clock and the courtesy car didn't make the noise. Also compared mine with two others in the family with the 2.0 tfsi engine and theirs sounds sweet compared to mine. Audi said to monitor the situation for another 1,000 / 2,000 miles. However I have taken the precaution of writing to them with a copy to Audi UK to make sure everything is on record.
A3 2.0 tfsi with lots of extras.