Why is the toyota rav4 making a whining noise?

On Your Toyota RAV4, the primary cause for whining when in gear is low transmission fluid. If the fluid is too low, then the internal components of the transmission are not lubricated properly. If the fluid is low, it's advised to check for transmission fluid leaks. The real thing You want to watch for here is a new whining noise. A bad input shaft bearing can create a whining sound when it begins to fail. This is an internal bearing within the housing of the transmission. Wheel bearings are located in each wheel hub, but the sound can travel and seem as though its coming from the transmission. Its more usual for a failing wheel bearing to create a roaring sound, but they can create a whine while driving.