When Sound > Speech is selected the A column is pronounced by the text-to-speech with a lowercase vowel sound 'a' '5' instead of 'A' '5' while all other columns are pronounced as the capital letter sound. When the engine is saying a full sentence like 'Knight to A5' it uses the capital A sound correctly.
For me any pawn moves on the a file have a pause between saying 'a' and the number. Any other pieces moved on the a file, or pawn moves on other files seem fine. Easy to test tis in the analysis board.