Squeal noise front left wheel whil driving will stop noise when you slow down or stop

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).

You don't say, Front or rear wheel drive. First check oil level, On rear wheel drive check the thrower plate on the tail shaft at the diff end is not bent and rubbing on the seal, A dry oil seal can make this noise.so can the U/Joints. on front wheel drive , check the cv joints , dry oil seals , the drive shaft inner cv joints have a thrower plate that may be bent. worn or binding brakes can make this noise also.

Sounds like a drive shaft U-Joint or a brake noise.

Get your brake pads replaced soon. Sounds like to me the squealers are starting to make noise. That is the indication signal to change the brake pads. Depending on how many KMS or MILES that are on your vehicle the drums & rotters may need attention.

Thanks for choosing FixYa and welcome. It sounds like it may be a brake pad. Chances are one of them fell off and that is why you no longer hear it. I would check the pads and the caliper also. Make sure the pads don't need changed and everything looks right Luke.

wheel bearing

Get the serpentine belt inspected or replaced.

To test open hood and while its squealing spray some water on it. If it subsides for a few seconds then you know where the source is.

that sounds to me like your brake pads may be dragging or your wheel bearing is shot

you need to check the front brake pads to see if the warning tab is touching the rotor ,this will squeal if the pads get worn out before it goes metal to metal, and if that is ok the only thing i would think of is the wheel bearing,

Do you know if he turned the rotors when brakes were done?