I have a Trane heat pump, model number XP14-024-230, and the homeowner heard the unit make a crazy…

I have a Trane heat pump, model number XP14-024-230, and the homeowner heard the unit make a crazy noise when it came on that sounded like fireworks. The contactor was being pulled in and then released and repeated very rapidly. The contacts were very toasty so I replaced the contactor with an exact replacement according to the ratings. The unit worked as it should but then after it ran for a while and satisfied the thermostat and then was called to come on again, it did the same thing. If you let it sit for an hour and then turn it on, it runs fine. All the voltages from the defrost board are correct and nothing else seems to be abnormal. Anyone have anything like this before?