Upon ice start up at times, there is a loud knocking noise emanating from engine compartment. Goes away after 10 seconds and car drives fine. Has occurred several times. Though there is a tsb issued, dealer would not fix unless issue is replicated despite showing them what my car did on video. Most noticeable after car was run for a very brief time hours before. Also notice the last few weeks, while driving vehicle, upon ice starting up, the engine is rough and the shift to ice is noticeable. Previously it was smooth. No codes have appeared and the car appears to run normal otherwise. I would like the dealer to fix the problem as described in 2 separate tsbs (engine mounts and intake manifold gasket).

- Cherry Hill, NJ, USA

The car suddenly decelerated from 65 miles an hour to about 5 miles per hour while driving on a highway at night with the shoulder blocked due to road construction. This same problem was present in the 2004 Prius and was apparently the subject of NHTSA investigation. There was a recall issued on November 30, 2010 for 650,000 units of the 2010 Prius. Toyota has not been able to determine the cause of this problem in the earlier models and admits it doesn't know the cause of the problem in the 2011 Prius. This defect presents a great danger, especially when driving in heavy traffic at highway speeds.

- Victoria, TX, USA

Upon starting vehicle, a very loud knocking noise, accompanied by shaking occurred. At this time no failure/warning lights appeared on dashboard. Moved car forward approximately 15 feet, and placed car in park, knocking/shaking did not abate. Turned car off. The next day, the car, upon starting had the same loud knocking/shaking. It was audible from several feet away from the car. On the second time, it was accompanied by a warning light to put the car in park. Vehicle was towed to the dealership.

- Albany, NY, USA