My car was recently in for a warranty job, and my courtesy car for the day was a TT. When I returned I commented to the Service department that the TT's turbo really whistled when accelerating (which I liked). They told me that by simply changing the air filter to a more free flowing one (such as K&N) on my A4 it would produce the designed sound. Can anyone tell me whether this is true or complete rubbish. Many thanks.