Rednaxela

ok so today i noticed while backing out of my driveway that i get a really wierd grinding noise when im moving at a very slow speed in either first or reverse, it goes away when i use gas and it makes no noise if i drift down or up a hill in gear or in neutral but when i play with the clutch to give a little push (i dont know whats that called) i get the nastiest grinding noise - it almost drove me insane at the drivethru today - what is it? its coming from way back in my car - is it my tranny? rear end? what is up with this!? thanks!

(btw i dont get this noise at any other speed than below practically 5 mph)