Random tire thumping noise

[Tonavi]

I just bought a 1983 Land Cruiser and have been driving on it all over without incident until today. It has 33x12.5 tires on it, too.

Anyways, when I was on 96 (a 50 mph road, relatively smooth), I heard this thumping noise coming from the front left tire. It sounded like a flat tire, and the noise is definitely coming from the tire (sounds like a puncture but it isn't). When I turn real sharp, it goes away sometimes, but there really isn't a pattern. AND about 100 feet from my house, the noise went away. I just went to get gas, and the noise was gone. On the way home, it came back.

I read online and a bad wheel bearing could be the cause along with a bad tire, but those are constant issues, not random ones. The truck was sitting all winter if that helps, but I inspected the tires and found nothing out of the ordinary other than a little cracking between the knobs, the tread is still good and there is no bulges or flat spots.

Any ideas?