This is usually caused by a difference in voltage from your system's ground and the ground on your cable. It is not unusual for the cable company to have faulty grounds. You should complain to your cable company and they will come out to inspect their cable. There are ground isolators that will stop the buzz but they sometimes degrade the picture quality.
This is a very common problem and any knowledgeable dealer in your area should be able to assist you.
This is a very common problem and any knowledgeable dealer in your area should be able to assist you.