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My '02 Prius, purchased in 9/02, gets loud when accelerating on the highway, usually above 45 mph. Also, it feels to me like it's straining until it reaches a higher speed, then it quiets again. In the city, just driving around, it's very, very quiet. I drove a friend's Prius, and hers did not make this noise. The car has been into the dealer three times for this. The dealership manager owns 3 Priuses and he's traded cars with me the last two times and driven my Prius into the dealership. He and the service manager agreed my car was noisier than others and the last time, a Toyota technician came over to the dealership and thought the noise was vibration from the exhaust. They took off the exhaust and repositioned it and all felt the noise was abated. To me, it's not much different.

No other Prius owner I've talked to has this complaint. Any experience with this?
Thanks!
 

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When you're cruising, the Prius is extremely quiet because it is essentially in "overdrive" (or the engine is off completely). In this case, the engine is running at very low RPM, typically between 1200-1800. When you need a bit more power to accelerate, the "continuously variable transmission" lets the engine have some "head", so it revs up quite a bit, to typically 3000-4000 RPM. The dramatic change in speed and noise tends to surprise new Prius drivers. Anyway, if there's something loose or rattling, the high power demand situations that rev up the engine will tend to make it more noticable.

In a more typical automatic transmission, the engine would stick to middle speeds until the power demand exceeded a critical value (running less efficiently in the process), then suddenly leap to extremely high speeds (5000-6000 RPM) when it downshifted to get more power. Then you'd really hear any loose parts.

So the Prius just seems dramatic under medium power compared to low power because you're used to a different, less efficient, harder on the engine transmission. But if your Prius is substantially louder than others, something must be rattling or straining somewhere. One quick check you could make is to verify that the oil and other fluids are at their proper levels, neither too high or too low. If the dealer agrees that your Prius is louder than other Prius under power, have them keep trying to diagnose the source of the noise. Loose, rattling parts could otherwise lead to trouble. But it is normal for the Prius to be much noisier when accelerating than when cruising. It's still quieter than other cars except the luxury models.

Robert Snyder
NJ-PIKACHU
 

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My Prius seemed excessively loud when I first bought it, particularly when going uphill or accelerating rapidly. I've found that over time(with more miles on the car) the noise has become quieter. Maybe 'wearing in the car' has something to do with it? Or maybe I've gotten used to it and I don't notice it as much now?
 
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