Don’t stress yourself. Take it to your nearest Holden dealer and book it in to be fixed. There shouldn’t be any problem in having it attended to.

With local production shutting down the big-car choices are getting fewer and fewer, but right now you can still buy a Calais if that's what you like. You can also buy an equivalent Falcon or Toyota Aurion. There are more expensive cars, from the likes of BMW, Mercedes-Benz and Audi etc. that would suit, but they come with a much higher price tag than a Calais. Others you could try are a Skoda Superb, a Honda Accord V6 Luxury if you're prepared to give up a little in size, and there's also the Chrysler 300C.

It's not something that I have come across, and I'm not aware of it being a known problem. Without being able to hear it it's hard to point you in the right direction. The dealer has done everything you would think of doing, but without isolating the cause. You could try changing the torque convertor, check that the brakes aren't warped, and replace the wheel bearings.