Same issue on my Panda . Default min volume for TA is 20, I would normally listen at something like 8 - 10. The only solution I found, well partial solution anyway, was to go to the user defined graphic equaliser setting and set all the 'sliders' to their minimum which has the effect of reducing the volume across the range -but also probably reducing the quality and definition of the sound as well. Now I can listen to the radio comfortably at about volume of 12 or 13 and the TA when it comes in at 20 is less of an increase on what I've already got.
I would have thought that a default of 10 minimum would have been more suitable - at least in the Panda.