makes a humming sound when on

[SIZE=3]Oven makes a humming sound while cooking on gas burners or oven and does not ignite gas tubes, you have to blow lightly on pilot light to make it ignite for oven use, this oven does not have electronic ignition, have scraped off carbon on the igniter then it does work for awhile then it goes back to humming again once the carbon buildup comes back, please tell me the steps I should take in order to stop the humming and ignition problems in oven[/SIZE]