This Batman is a mouth-breather, plain & simple.
And it was very distracting.
“What’s with Batman’s voice in ‘Dark Knight’? – CNN.com
Reviewing the film for MSNBC, Alonso Duralde wrote that Bale’s Batman in “Batman Begins” “sounded absurdly deep, like a 10-year-old putting on an ‘adult’ voice to make prank phone calls. This time, Bale affects an eerie rasp, somewhat akin to Brenda Vaccaro doing a Miles Davis impression.””