[burnin oil]

Since loading the suspension seemed to help the situation you may try greasing the driveshaft and ujoints. Maybe they have some rust build up and loading the suspension helped. This is a long shot but I have heard ujoints squeak or make funny noises on equipment. My dad had a blazer that randomly would yank the steering wheel out of your hand and make a hard turn. After lots of head scratching and parts swapping it was a partially frozen u joint in the front axle that would grab and bind. Strange things do happen and grease is cheap.