What is the cause for noise coming from faucet when the water is turned on?

Probably loose washer. What kind of faucet.

Not sure of name brand but it has both a hot and cold knob. It makes like a humming noise no mater which one you turn on.

Is the noise on the cold, hot or both sides, the best thing to do close both angle valves under the sink open one at a time see what happens, you may have loose washer in one or both angle valves as Harold says, and there is a posibality of bad stem washers, let us know,Thanks.

John

Yep and sometimes it is the washer in those angle stops is the problem. It isn' always the faucet, it can be the stop too.