Just a guess but maybe you have a vacuum leak? Try to locate the buzzing with the engine running. If the location of the noise isn't obvious, try using a tube on your ear like a paper towel roll. If you can locate the buzzing, that may be the source of a leak. Vacuum leaks can make your idle rough and cause fuel mixture problems. If you're handy and have some basic tools, you may try to pull the spark plugs and look for anything unusual, including the insulator tip color.