Hi had my DMF, turbo/manifold done. But now get a rattle from under car that dealers say they cant hear and bad smell of fumes at low speeds and idle. do you think they have damaged the flex in the CAT? checked for leaks under engine cant see any?

Im sure dealers getting really P155ed off with me, ive been hassling them for 10months about my dmf, then finally they hear the rattle. they hate me, they even look at me funny. i dont want to go back as they make me feel like im wasting their time