Assuming your car is fitted with a manual transmission, this could be as simple as a gearshift linkage that has jumped ship, or a selector cable that has stretched or snapped. If that’s the case, you should be able to look from underneath the car to see what’s hanging off or missing and not connecting the shifter to the actual gearbox. If the shifter moves freely inside the cabin, but doesn’t sound or feel like it’s connected to anything, that’s probably the case.

If you’re unlucky, you may find that there’s something inside the transmission (probably to do with the selector mechanism) that has broken, worn out or failed. In that case, you need to go inside the transmission to see what’s what, and that’s a much more complex task that involves removing the transmission from the car and lots of labour.

The automatic transmission is a mysterious, marvellous piece of equipment that manages to work almost in spite of its complexity. Guessing at a problem like this is fraught with danger, so the best advice is to get the vehicle to a transmission specialist, download the fault codes and see if they give the technician any hints as to what’s up.

Transmission problems with this make and model are hardly unknown, so avoid driving the vehicle any farther until it’s been looked at. You may end up doing more damage by continuing to drive it.

The actual problem could be anything from a transmission that is about to catastrophically fail, to one that has simply lost its 'memory' or programming and can be rebooted fairly easily and quickly.

Conventional wisdom says the first place to start looking is the turbocharger and its plumbing. A turbocharger operates at very high speeds and a whistling noise is quite common. What you shouldn’t have, however, is a loud version of that noise, or a whistle that is suddenly louder than ever before.

Cracked or leaking turbo-plumbing can allow the noise to escape, but a turbocharger with a worn bearing can also suddenly become louder in its operation. So that’s where to start looking.

Why does the noise drop in the higher gears? Perhaps because you’re cruising in those gears and not accelerating hard as you do in the lower gears. Less throttle input means a slower turbocharger speed and a drop in turbo volume and pitch.