Low-level grinding/vibration occurring on my 2016 Mazda BT-50 through the steering column

The steering system in your Mazda is the old-school hydraulic type, rather than the more modern electrically-assisted set-up. Noises when you turn the steering wheel often indicate a problem with the rack itself or the hydraulics, either of which can make the system grumble and rumble when you deflect it from the straight-ahead.

The first thing to check would be the hydraulic system for leaks. These will show up as drops of fluid seeping from the various joins in the system. A check of the power-steering pump's fluid level is also a good indicator of a leak somewhere; if it's down on where it should be, you have a leak. If that's the case, the whole system probably needs a once over.

You should also check the actual steering column for the source of the noise, as sometimes a simple plastic-on-plastic contact somewhere on the column or its shroud can produce a noise like this.

Within the rack itself are valves and fluid passages that can, over time trap air. When that happens, the air bubbles can make the sort of noise you're hearing, also. So before you spend any money, try this trick: Start the engine with the car stationary and then cycle the steering from full left lock to full right lock a couple of times. Often, this will bleed the air out of the system and restore things to normal. It may or may not work, but since it's free, it's worth a crack.