Three months ago the outside unit stopped coming on and I replaced the capacitor which tested bad. After that the unit worked fine, but I started to hear a high pitched vibration just before the unit would turn off. This occurred randomly so I was unable to pinpoint it and. Now the outside unit, either does not turn on at all , or shuts off after about five minutes of being on leaving the inside unit to run continuously pushing warm air. The unit is a Carrier 38TRA about 12 years old. Contactor was changed 6 years ago. Any help would be greatly appreciated.