My car is CLS 2002. My friend replace front brake pad to new one. When I push the brake there is no sound. However, there is noise when I just drive. It will disappear? or it is a problem?

It is a problem.

Please explain why its a problem, instead of scaring the fucking guy.

Seung, without seeing the car, we have no clue if it is a problem or not.
its hard to diagnose something, we cant see, feel, or hear.

if you are worried, please bring it back to your friend who did the job, and he can inspect it.

Shouldn't he be scared? It is a problem because the brake pads are either not installed correctly or they are the wrong pads or there is some other problem with the braking system, and the car may not stop when needed.

Thank you guys. I will check it with my friend.

there isnt many ways to fuck up a pad install.

if he was in danger, it would have already happened.

Just pads were installed? Sounds like a high spot on the rotor contacting the new thicker pad material. May go away after the pads wear into the rotor some.

The fix is to get your rotors turned. Then bed in the brakes. Youtube the procedure.

^but we dont know whats going on...
you cant really recommend something if you dont know whats going on.

some one needs to inspect the rotors and pads to determine the next course of action.