Subaru Repair: outback wagon, outback wagon, pitched whine

Question
revving the engine in neutral does not cause the sound. It seems directly related to acceleration and deceleration, but not to speedometer/tach. Can't tell if the sound can be heard outside the car; couldn't convince anyone to sit on the hood while accelerating. thanks
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-----Question-----
I have a 2001 outback wagon w/ about 50K miles. When I step on the accelerator it emits a high pitched whine...does not seem directly related to speedometer or tach. Constant accelerator pressure yoilds constant whine, increaded pressure increases volume of the whine. Any ideas ? thanks
-----Answer-----
Can you hear the sound while you are at idle and reving the engine? Or, only when moving? Coming from the front or back of the car? Can it be heard outside of the car?

Noises are tough to figure out in person, and almost impossible here. But, try answering the above questions and we will give it a shot.

Answer
Have you had your brakes checked lately? If the noise is coming from one of the wheels then it could be he wear indicator rubbing the brake rotor. Also, the backing plate may be bent and rubbing the rotor, and my final guess would be a rock between the rotor and the backing plate.

If the noise is coming from under the hood check for a loose hose - like the air intake tube from the air cleaner to the throttle body, a bad pcv valve, or maybe even the air cleaner box not correctly closed. I replace and air filter one time and did not close the box correctly and it took two visits from the customer to our shop to figure out where the noise was coming from.

good luck.