1991 ford explorer

I have a 1991 ford explorer, when i driving down the road it sometimes wants to kick in four wheel drive and makes this whinding noise, till i stop the car, then i get going then it starts again i do this for about 5 time then it stops, its driving me crazy, also when i try to put it in four wheel drive i press the buttun and i hear a loud clunk and sometime the four wheel drive dont go in and some times it does please Help

your automatic hubs are bad. i suggest putting in manual ones.

Sounds kinda more like a transfer case problem to me. Case wears and the the shift fork moves around trying to go into 4wd. Very common. Also the oil pump wears a deep goove into case, so that will have to be welded or new case half. Thats just kind of a guess as I'm not in the rig to feel it myself. Auto hubs would have to really be broken up to try to lock in. They seem to not unlock rather than lock up by themselves. Just things I see in the biz.

Stay cool.