Technician inspected furnace operations. Found that sounds of vibrating were intermittently being caused by air gap at furnace door and around filter rack. Filter rack was upside down allowing more air to bypass. Blower capacitor was slightly weak at 17 µF instead of 20 so along with reducing air leakage technician, replaced blower, capacitor. Furnace is operating very well. At times when the unit starts or stops there is a slight sound from the ductwork flexing however, this is not excessive.