I was told NOT to put an additive like Transmax in there when it's still under warrany as Ford will try and void it if they find it (but not sure if they can tell or not?). Apparently it's an additive and is not factory recommended. All of them make a little noise at low revs, but there's definately as issue with yours. I would take it back in and be firm with them. Tell em you don't want the car back until they have fixed the problem, and if they don't fix it, ask to speak to someone else, and if they can't help you, ask who else you can speak to. If you don't give up, they'll have no choice but to spend some time dropping the box and investigating it, not just trying to 'insulate the gearstick' and muffle the sound. What a fukin idiot.