I have experienced the same thing.. and still am.....
I have 2 boxers. Oxford is not afraid of anything.
Snatch.. on the other hand.... I picked up the most outgoing puppy of the litter. He was not fearful as a pup'. The one day, i guess the famous "fearfull stage" he became scared of... cars with open doors... then it became trucks, them cars with hood open, then boxes, then it was men, then loud noises, .....
I read lots of book. Since puppy, i have taken snatch everywhere... stores, dog parks, equestrian center, neighborhood...
It has gotten better. He is fine walking pass cars, open doors, trucks.. he's good now.. i spent afternoons, just him and me, going sit by cars and trucks in parking lots
Still loud noises are a problem.... he's scraed an dwill run away.. this makes it dangerous for me to leave him off-leash sometimes...
good luck with your baby!