1993 Chevy Truck four wheel drive

I put my truck into 4 wheel drive today, had clunking noise from front end. started driving around 35 when you let off of gas the noise turns to a grinding noise hit the gas again noise is gone. When coming to a stop the noise is there the whole time. Taking off again starts banging and clunking again. Checked all fluid levels all are ok, brand new tires and new transmission. everything work fine last season this truck has a snowplow. thanks for any help you may have