Continuous squeaking/whistling sound from the rear

Dear Pros,
recently my car(KIA, Avella Delta, 1998) has been giving this odd sound from the rear tires, it's like a highly pitched squeaking/whistling when the car is moving, even I have changed my rear and front brakes after hearing this odd sound it is still squeaking.
Another thing to be noticed is that when the car goes fast the sound stops. When I press the hand-break's button -and keep pressing it while lifting the hand-break a bit- while the car is squeaking the sound goes off.

Please answer me, my mechanic isn't capable of solving this problem, I seek your guidance.