do you have the metal brake pads? they shouldn't squeak for prolonged periods though... hmmm
the metal pads can squeak on wet rainy days. Are you sure its not the rear brakes squealing? find out which side is squealing by jacking the car up and spinning the wheel. if it doesnt squeal, spin faster
If it was the tranny should it not stop making noise if the tranny was disengaged completely? (Neutral and clutch in)
you should NEVER DO THIS, but I raise the car securely on stands, start the motor, and put it in gear. Now you can go underneath like an idiot, and find the source of noise
If it was the drive axle shouldn't it make the same noise regardless of whether the car is moving forward or reverse?