I have a 2002 ford explorer that is making noise (a howl and knock) at higher speeds and when I let off the accelator it gets worst... The wheel bearings have been replaced on both sides in the front... Then if I shift it into 4X4 the knocking and howling stop when going down the road but when I let off the gas it like really whines as it is slowing down. I pulled the front cover off the pumkin up front and dont see anything, was thinking maybe I could pull out the spider gears and just do away with the 4 wheel drive, but dont really want to do that. When there was snow on the ground it almost acted like the auto 4 wheel drive was kicking in and out like it was detecting slippage... I do alittle work on cars but nothing computerized. I thought maybe it was a wheel bearing again, but when you put it into full time 4 wheel drive it goes away until you are slowing down... Any help would be appreciated. Thanks