I have a 2015 Isuzu MU-X. I have heard a whistling noise which was intermittent. It sounded like chains dragging on the ground when towing a trailer...

Blown turbochargers are hardly an unknown problem on the MU-X or many of the other popular modern turbo-diesel engines that work pretty hard and make lots of horsepower and torque for their capacity.

Some owners report a rattling, metallic noise such as yours; others reckon the sound of a dying turbocharger is more like an air-raid siren. Either way, the turbo needs to be changed sooner rather than later, to avoid the chance of bits of broken turbo being sucked through the rest of the engine with catastrophic results.