Good luck....I believe it is a vacuum leak...somewhere on engine "thingies" ..Unfortunately, it is intermittent , but always needs to be "heard" while driving...Not sitting still...This is why I think the service depts are going to pass on it...unless it happens during any short test drive they perform...50/50 chance...and mine seems to need 40-50 mph to occur...My dealership is located in congested area of roads...and past experience, they do warn "they do not drive it at hwy speeds to evaluate"...Good luck with your visit...and I hope you will post the results...