2007 Chrysler 300

Go to auto-zone let their employee read the code.

I did the code is p0456 evaporative emission system leak detected ( very small leak) for predetermined period of time

Would this cause my car to have a humming noise when I get to 30 mph

My first thought No. Vacuum leaks sound more like a hiss. If it is making the sound humming at speed only I would say no that is not it cause you could replicate this humming while parked , engine running and holding the RPM's steady and if you not then you know that is not it. I do believe it would be best to locate this leak and repair it. The hum is a separate issue I believe. Hums are most likely wheel bearings, drive shaft, differential. Is the hum from under the car or does it sound like it is from the wheels? Can you also feel this hum? Vacuum lines can produce load hisses so it could be described as a hum, I would locate it and rule it out. Brake Boosters can make noises when they leak pressure. you should hear it all the time or just when applying the brake. Sometimes a pulley can make noises too. The Drive shaft where it enter the trans can become worn and the hum will become worse and need replaced as to the rear differential, may could also check the gear oil level of the diff. Do you have a lot of miles on it? A diff or bearing or drive shaft will hum will turn into a roar, Transmissions can go bad too and sometimes whine before going out. Like the engine pulleys if it were that or water pump or main crank bearing you could replicate it sitting still.