I have an 01 RD688 Dump and it mostly does it when I'm loaded but when I turn sharp I can hear a popping sound coming from possibly the front drive axle. I'm not sure if its a bearing or possibly some splines slipping. I figure if it was something with an axle or rear end it would do it all the time and not only when loaded. I've heard bearings can do that when they are under a load and going bad. Its not a low thud pop but somewhat of a high pitch pop (yes I know this sounds crazy). It will do it a 3 to 4 times in a turn then stop when I straighten out. Suspension bushings were replaced mid last year. King pins and tie rod ends replaced a couple months ago. Ive crawled around and pulled and yanked on everything, all drive shafts, U-joints and torsion bars seem good and tight. Has anyone had this and what was it? Thanks.