Going back and forth between the dealer and your local mechanic seems to be a waste of your time. So far, the dealer has told you what the noise isn't , and the local guy has told you what he thinks the noise is, but doesn't want to get involved!

It's simple. Let the dealer diagnose the problem. If they're wrong, don't worry about it. Let them know that you're not going to pay for them to guess. Tell them that you'll gladly pay for a proper diagnosis, but you won't pay them to "try this or that and see what happens". Let us know what happens.