94 Ford Ranger 4x4 V6 4.0L automatic locking hubs (push button) 4x4

It recently took my ranger out and put it in 4 wheel drive, when doing so after about fifty feet I heard a loud clunk. And it keeps on clunking as I drive it more. (You can feel it also) like the 4x4 is engaging and disengaging. Or something like that. It drives fine out of 4x4.
Please help,

Thanks - Tim

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TIM WITH (THE RAVEN)1994 FORD RANGER XLT SUPERCAB 4X4, 4.0L V6, 5" SUSPENSION LIFT 33X12.5 MUD TERRAIN TIRES, ORIGINAL OWNER