Noise when in 4 x 4

A grinding or rumbling noise can also be symptoms of a wheel bearing or constant velocity joint in a driveshaft. A worn wheel bearing can also cause a 'whistling' sound (as can a worn CV joint).

A grinding noise with brakes is either worn pads causing metal to metal contact on the brake disk/rotor, or the brake backing plate catching on a spinning rotor ... or a loose/missing anti squeal brake shim (they stop the pads from rattling and vibrating).

However, as you say a mechanic has looked at the brakes and can't find anything wrong .. I think I would begin to suspect a wheel bearing or constant velocity joint on the driveshaft (front wheel drive cars).

There are a few possibilities.
The brake pads have worn down and there is now metal to metal contact with your brake disk/rotor

The driveshaft is worn

The wheel bearing has worn

A grinding noise - when braking - is usually associated with worn brake pads.

If the grinding noise is there while you drive without braking, it could be the brake pads/rotors, yes .. but it also may point to the wheel bearing or driveshaft itself.

You can raise the car, after removing the wheel, and look at the brake pads/rotor.

However, sir, if you can't do these mechanical things yourself, please do go to a workshop. The value of your life far outweighs the cost of repair

ok, think about mass that moves under the forces of braking, things like engines and gearboxes, have you checked all those mounts for integrity, have a look to see if anything has been rubbing, new shiney spots appearing that weren't there before.

something is not aligned right take the wheel off that is causing the noise and check the carriage

Grinding is a sign on brakes in need of replacement. Your pads are worn through and now the metal backing plate of the pad is grinding up against the rotor. Replace the pads and rotors asap to prevent further damage.

Hello i would check your wheel bearings or sometimes called bearing hub .Jack car up prop the car with axle stands now remove your tires and rotors once removed wiggle you bearing hub left to the right your bearing hub should have minimal play one side to the other is obvious the looser play hub will be your noise you have been experiencing.most people call this road noise.

Does it happen all the time or when brakes are applied? Usally a bad bearing will cause a growling noise. I would check both the brake pads on the right side. Often the inner pad will wear off, then you have metal against metal, causing a grinding noise.

when turning left vehicle distributes weight to right front wheel bearing causing load. since u describe a noise in right front while driving straight i would suspect failed right front wheel bearing. see if your noise changes/goes away while turning right that should tell u 4 sure

Sounds like the pads are worn out and are grinding on the rotors. You will likely have to replace the pads and rotors.