It sounds to me as a most definitely a rotational sound . If you push the clutch in , while in third gear, does it Lessen , or possibly stop ? Oh Yeah .... the front drive shaft does not spin unless it's not in neutral . Your TC shifter position alows the front shaft to engage or disengage. You could have worn TC linkage detant balls & springs , causing your TC to be in 4W high , & your sloppy front shaft to be the cause. Remove the front shaft & run it again. That's a start, cause it needs rebuilding any way.