97' expadition

has A4WD i switched to 2H at about 30 MPH ALWAYS DID even at higher speeds, but this time, Bang and a wizzzzz i slowed and enterd a parking lot and circled the lot a min , tried stopping in park and Nutral as i tried the switch at all ranges nothing did anything as it should have, i wasnt far from home and figured to head home only to pull onto the road and could only maintain 2K at 20mph the 1/2 mile home, when i let off gas it would bang a bit and make noise ,fluid great levle was changed along with filter a year ago? was told mayb this mayb that? a friend of mine is capible of such repairs but cant for about two weeks i figured any more info that i gather may help him help me when he can, thanks in advance