Shy dog question

Hello,
My son just got a Chesapeake Bay retriever. He got him for free as the guy said that the dog was gun-shy. Well, that is the biggest understatement that I've ever heard. This poor dog is scared of everything. DS got him on Thursday but the two of them have already bonded really well. He's nine months old and almost bigger than our collie.

The problem is that this poor dog jumps at noises that you wouldn't even consider loud. DS was grilling a steak on the grill last night the the dog just about jumped to the ceiling when a briquette popped. Can anybody recommend a book or have some advice on helping this dog get over being so scared?? I'm wondering how he was treated by his previous owner. He supposedly had $600 of obedience training, but I really wonder. The previous owner gave him back to the breeder since he is so scared. DS has been considering getting a dog for some time and he was offered this dog because the breeder wanted him to have a good home.

I dropped his bag of treats on the floor and the dog cringed and peed on the floor. I have never seen such a reaction just from dropping a wal-mart bag of dog biscuits. I would really appreciate any advice. Too bad the Dog Whisperer lives so far away....

Thanks in advance.
Ruth