One problem related to loud engine noise has been reported for the 2007 Toyota Prius. The most recently reported issues are listed below.
We noticed the red triangle light and so we checked the engine oil. The dip stick was dry. I put oil in the engine and the red triangle went away. I kept an eye on the oil level occasionally I needed to put more oil in the engine. 3 months after taking the car for a regular oil change at the Toyota dealer the red triangle came up again and this time I spoke to the dealership about the issue. The response was that it would be expensive to repair the car and the best solution was to buy a new car. I was never told about the 2011 TSB for excess oil consumption that Toyota had issued. Today, July 17th, 2020,I called the dealer to ask about the TSB, and I was told that the TSB has been out for 10 years so I had had until 2017 to qualify. I do not believe I ever received a letter notifying me about the issue. Had I received the notification I would been the first person in line at the dealership. Also, my steering wheel feels like it is loose, if the speed is over 45 mph it feels unsafe, the slippery sensor light comes on when I am turning the wheel slightly on a dry road, and there is an excessive noise inside the car even with the windows closed. This happens during highway driving. I am about to donate the car so that it can be used for parts. I love the car now I know to check with NHTSA when I purchase my next car.