I have a Mitsubishi outlander 2005 model. The problem is , it makes a grinding noise from the left wheel while braking. The noise comes as if some thing is grinding on a small portion of a metal disk in every rotation this happens only when the vehicles is braked during slow speed and only if the pedal is half way depressed. On sudden brakes, this doesnt happen(or no time to happen??) please help

Can be a wheel bearing or the wear indicators on the brake pads beginning to touch rotor. https://www.6ya.com/callphilipforhelp

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).

It's a good chance that it's either wheel bearings or the CV joints.

It very well could be the strut.
smaller chance could be the CV axle.
Also have the splash guards/heat shields checked to make sure they are all tight in place.

I had some issues with my 2005 explorer left rear. It was making a creepy old door sound at low speeds and then a high pitched whisel at high speeds. That turned out to be a broken wheel bearing and had it replaced. Note each wheel has two wheel bearings. After that a new noise developed that sounded like metal scraping/ grinding metal. It end up being the brake dust cover got bent when they replaced the bearing and it was rubbing something, the fix for that was bending it so it didn't rub. I hope this helps.

Have the front brake pads checked for wear and also have the CV joints checked.

check the axles outer cv joint and wheel bearing too. One is causing this grinding noise

I would guess wheel bearings. does the noise increase as you go faster? Altima wheel bearings are common. If this is the case go ahead and replace both sides as the other one will go soon as well. I hope this helps and good luck.

Without looking at it, you may have one or more of the following:

Rust on the inside edge of the rotor (most common)

Worn front brake pads

Front wheel bearing problem.

Backing plate (behind rotor) rubbing the rotor

These are the most common causes, you can see 1,2 & 4 with the wheel off.

Hope this helps.