I was having the same problem when I first got my new bike. The difference is that I was sure, as was the LBS wrench, that it was coming from the front. LBS wrench checked everything mentioned in this thread and the rattle remained. He then replaced the front wheel and the rattle remained. He then replaced the rear wheel and the rattle disappeared. The one thing I learned from this is that it's almost impossible to isolate the location of a rattle. I and the LBS wrench would have sworn to our graves that it was in the front yet it turned out to be from the back. At some point it becomes just a process of elimination.