M.M.
I know exactly what you are experiencing! My son is 2 1/2 and he was/is extremely sensitive to loud sounds - lawn mower, trash truck, vacuum, anything that startled him. I read the book "Highly Sensitive Child" by Elaine Aron and it helped me understand my son better. He is not completely like the children described in the book but I took away a greater understanding of how his brain works and what I can do to help him. For my son I had to face the loud noise with him and show him it was okay - in time he was able to identify the noise and understand what made it. He is doing much better now but from time to time we still have to face the noise together. Hope that helps!