I've got a 94 Mazda B2300, 131000 miles.I drive it on the freeway at normal speeds, take my foot off the gas to let someone merge or something and then put my foot back on the gas I hear a load bang. Sort of like a hammer hitting metal. Doesn't make the sound in 1st 2nd 3rd or 4th just 5th gear. Crawled under and all the mounting bolts / structures appear solid. The drive shaft has about 1/4 inch of play in it with the car parked in neutral (I know it's not good to get under with it in neutral but I blocked the tires.... Is 1/4 inch of play normal...??? Any other thoughts on what it might be....??