Whenever I raise the gar up on jack stands, and put the trans in "Drive, reverse, 1, second" and lightlly step on the gas I get a wooshing sound from under the car. Now when I get the car in the street, and drive it a little, no noise can be heard. Are the differential bearings hard to install, do you guys recommend taking it to a shop ? what's the cost ?
If you're talking about the axle bearings, they're pretty easy to install but time-consuming. However, are you sure it's the bearings? Can you make the noise happen by rotating a wheel by hand? Can you wiggle the wheel side-to-side? You might want to have someone else lightly hit the gas while you try to pinpoint the noise.
If you've already figured out the noise, can you tell us why you think it's the bearings? I'd hate to see you replace the bearings but not get rid of the noise.