the milkman in our street comes at that time - you must be a very light sleeper to wake up. I'm a light sleeper and it woke me up for the first 3 months we were here (didn't have a milkman at our old place) but after a while, I got used to it and slept through.
Don't go to bed earlier, it will just cement your early waking up routine. Keep going to bed at the same time - close all your windows, get thick curtains and eventually, you'll sleep through it (though it will probably take some time).