Rather than wash and use compressed air... there's a product called "Brake Clean" you can buy from places like Super Cheap auto. Pull the wheels off and give the brakes a good going over. If you're inclined, pulling the pads out and giving them a squirt can also help. This type of squeel generally lasts the whole time you have the brakes applied no matter what pressure and will get more noticable at lower speed.
If it's not dirty on the front of the pads, it may be dust behind them moving them off the backing that the piston applies pressure to. This backing on the pad could also be damaged. It's often the cause of brake squeel as the pads vibrate across the caliper under braking. Your dealer will be able to fix this for you and it should be no charge. This typically only makes a squeel as you're coming to a complete stop under moderate to low braking force.
Another cause of brake squeel can be a lip that's formed on your disk rotor. Run your finger from the inside of the cool disk to the outside and see if there is an obvious lip when you reach the outside. If there is, you can ask the dealer/service agent to remove the lip, but you'll have to pay as that is wear and tear based on the way you drive. with this type of fault, the brakes will squeel under light pressure, but not generally when you brake hard.
I think it's unlikely your disks are glazed... which can also cause a squeel and requires the disk to be machined to return to having a rough surface. This type of squeel will happen pretty much any time you hit the brakes regardless of pressure applied.
