I so feel your pain. I have a one year old little girl that is a lot like your little guy. She isn't afraid of inside noises (except vacuum cleaner) , but , is terrified of all outside noises. She is terrified to the point that she WILL NOT go outside. She will go outside after dark , but , only goes outside the door and just sits there. If while out there she hears a car , dog , train, etc. BLOCKS away she immediately starts jumping on the door wanting to go in. I have a fenced in backyard , so , it is not like something or somebody has scared or threatened her. And I am ALWAYS outside with her if she will go out. I have a three year old poodle (both of my dogs have been fixed) that will go out anytime I open the door for them. She follows him everywhere except outside. If anyone comes in the house whether she has seen them before or not she is IMMEDIATELY gone. Never to be seen again until it is just us here again. She wasn't like this when I first got her at 14 weeks. She was very well socialized with kids , adults and the outdoors. But , for the last several months she has been this way.
This is why I say I DO feel your pain. Hopefully we will both find answers to this problem.
