Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
This can be a very annoying issue for you and there are many tips to help stop this behavior.
This LINK ( http://www.humanesociety.org/animals/dogs/tips/how_to_stop_barking.html#.UvuOH7Tw1c4) will give you 6 steps to stop your dog from barking by removing the motivation, ignoring the barking which gives Jack the attention that he craves, desensitize Jack to the motivation , keep Jack tired by increasing exercise and have him wear a DAP Collar. This is a canine pheromone that acts as a calming agent and will help Jack past his anxiety.
The most effective but aggresive measure is to purchase a good Ultrasonic Collar such as the Innotek that detects when Jack is ready to bark anfd gives a high energy sound or slight shock that will stop his barking. This may seem cruel but it only takes one time for Jack to get the message. LINK
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, Dr. Loretta