Whenever I turn off my 05 HAH while it is still in Drive instead of Park, it always makes a "pop" the next time I start it. I figured that turning it off in Drive must leave it something in some unfinished or unresolved position, and so it makes this noise to resolve itself when starting it the next time. So I stopped turning it off while in Drive, and I don't get the pop upon starting. I suspect that it is not designed to be turned off while in Drive. If you ask the dealer about it, please post here with what they tell you.