Bad noise when motors switch

My 2013 Prius v 1,400 miles did the same thing on a cold start. It sounded like something really bad was happening. It happened once last week and hasn't happened again. This is my first Prius and I know little about how they work but I suspect this has something to do with the the system starting the engine which usually happens a few seconds after I put the car in reverse to back out of the driveway.

 

Same thing happened on my 2012 Prius v at around 4000 miles. Violent shaking and knocking when the ICE started after backing out of my garage. I shut it off then restarted and it shook again. The third time starting it was fine. I reported it to the service mgr at my dealer and he thought that maybe some water had gotten into the ignition system. The previous day I had washed my radiator with a hose running at a low flow rate to clean it after a 3000 mile trip.

In any case the car now has 8000 miles and the incident has not repeated.

 

there are quite a few threads on this. it happens, nothing to worry about.

 

I've had this happen a few times now as well. 28,000 km on my v.
First time it really freaked me out! Happens at anything from +5 to -25 celsius.

I've learned a simple trick to prevent it happening from another comment in the gen 3 forum.
Whenever powering on from a cold start just press on the gas pedal (no more than halfway down)as soon as the ready light stops flashing. Engine always starts up smoothly and with no knocking when I've done this.

 

Going to guess the knock or noise is most likely water in the gas caused by the cold and phase separation of water/gas when it is an ethanol blend.

Fuel School: Phase Separation in Ethanol Blended Gasoline

If you are using a 10% blend, try switching to unleaded only if available in your area during colder months and see if the noise goes away.