I have a newer HVAC unit that was installed 2 years ago. The outside unit has always made a buzzing sound when kicking on. Lately, however, it seems to have gotten worse. It not only buzzes when kicking on, it also has a periodic, shorter, buzz that occurs while running. It makes a typical humming noise that seems to be pretty loud (although can only be heard while outside), but this buzz is really loud and can be heard inside the house.
