It is very interesting to see this and most other reviews focus on criticizing the CVT gearbox and lack of performance, for all Toyota/Lexus Hyrbids. At times, its a statement which they could easily make even with out trying the car..Also, the reviews on hybrids are done on just one drive, considering the engine and class is different and does need knowing the car more before jumping to conclusion! Which most reviews do..
Going back to it, the car has gearbox which has potential to become a bit noisy when you are pressing the throttle hard, more prominent if one is going over the speed limits quickly (e.g. overtaking). The noise is not disturbing in any ways..The key message is if you the car is driven within the normal speed limits , the car should give good MPGs and reasonable performance.
I have kept Prius before this Lexus and have never felt that the performance or noise are issues any ways!
Hope that helps