It's been a while since I followed priusonline, and I seem to be foiled searching for this problem, since the common word filter won't let me search for phrases like "engine noise".
Yesterday, as I was leaving my in-laws' house, my 2002 Prius started making a loud noise with vibration, almost like the noise when you veer off a highway and hit the rumble grooves (at first, I thought it was more of a grinding, but after hearing it longer, rumble grooves seems closer to the sound). I stopped, checked for flat tires, checked for stray tree branches hanging on for a ride (wooded gravel driveway; it's happened before), and found nothing. So off I go again, and it continues to make the noise. It seems to vary with engine speed, and when the ICE shuts off, no noise. When the ICE is slowing down, the vibrations really shake the car. I stop again, and this time I look under the hood and confirm that I still have engine oil, coolant, etc. No problems there. Frustrated and not wanting to be stranded an hour from either house, I turn back. Immediately upon turning back, the car returns to its normal self -- no funny sounds or vibrations the entire way back! At no time did any warning lights come on; it was maybe two miles each way.
Has anyone out there experienced anything like this? Any theories? For the time being, I've swapped cars until I can get back to it next weekend and see how it's behaving.
The only theories I could come up with were a failing engine water pump, or a rock stuck in an engine mount. Will a dead water pump trigger any warnings before the engine overheats?
