Humming usually means a bad wheel bearing which gets louder with speed.

Excessive brake dust means a seized caliper. Rotors can warp from the heat causing vibration.

Exhaust noise is proportional to RPM, so if you released the gas (or floored it) @ 55MPH, the sound should change.

 

how safe is it to keep driving the car if there is wheel bearing noise? Should I get it fix right way or it can wait a little bit?

 

Wheel bearings generally will get noisier before they fail.

I would suggest planning on dealing with the brakes and wheel bearing at the same time as some of the same parts need to be removed.

If when you hear the noise, if you gently put a little pressure on the brake pedal, does the noise change?

How are your tires? Good way to check them is to rotate them. If the noise moves, it probably was a tire.

 

When I press brake, the noise seems goes away. Not quit sure, cause when I hit brake, it lower the speed, and no noise seems less. My tires looks fine at least looks fine by me.

 

When I press brake, the noise seems goes away. Not quit sure, cause when I hit brake, it lower the speed, and (no) the (?) noise seems less. My tires looks fine at least looks fine by me.

That does sound like a bad wheel bearing.

I'm thinking that the brake disk is mounted to the hub and the hub is held to the spindle by the bearing.

When the brake pedal is pressed, the brake pads move the brake rotor enough to take the pressure off of the wheel bearing and the noise goes away.

 

You can jack up the front, then spin the wheels and see if one drags.

Also, grab each wheel and try to rock in multiple directions. Spinning a wheel and holding the spring can also let you feel bearing issues. There are a lot of how to videos on this if you goole things like "how to diagnose wheel bearing," etc.

 

I just like to give a update on my wheel bearing issue. So now, I see lots of dirts/mud on/only on my right front wheel. Is that confirms bad wheel bearing on right front? or just bad tire?

 

Is it on the inside sidewall surface? That's a sign of a burst CV boot. The grease flings out and lands on the tire.

 

Wheel bearing noises often change when you steer one way or the other.

 

No, I saw dirt on outside of sidewall. Have to double check tomorrow.

 

Check all four tyres that you don't have a bolt/nail stuck in one of them.

My '93 Camry made a similar noise and I suspected rear wheel bearings, until I checked the rear tyres and found a bolt sticking out of the rear LHS.

Cheers,
Tony