Mazda pickup makes scary sounds

I have a '97 Mazda B4000 (4x4) pickup. Recently, it has begun making loud, fast clunk-clunk-clunk sounds that shake the whole pickup. After a fearful 15 - 20 seconds, it goes away and all is "well." Today, it made that sound, but later in the afternoon, something that sounded like the rear tires were being rubbed on by something began......... I came to a stop-light and there was a "clunk" and then it was fine all the way home. what might be the problem here? Transmission? Drive Shaft? Can you help? hi. you can test for alot this way... have someone start the truck. with their foot firmly on the brake, shift back and forth from drive to reverse. if it does not make any noise, then park it, and jack up the rearend. [truck turned off] in netural, turn your tires by hand. they should only turn around, they should not move side to side. is the sound effected by the brakes? let us know. Car Repair Talk's forum.