I have noted some intermittent problems with the driveline. Last week, the I felt a strong vibration coming from just behind the center console when driving in a parking lot. The noise went away and did not reoccur. Then, last night I began to hear a metal-to-metal screeching noise that was speed sensitive in nature. It also went away and did not reappear. But I do notice that if I have the radio and heater off that I can occassionally hear a faint squeaking noise from the driveline. What could it be? The car has 143k kilometers.