i recently replaced my rear u joint which was really worn out and causing a bad vibration. drove the truck for 2 weeks and the vibrations came back. i assumed that the u joint went again due to having the same vibration and humming noise in the rear end. brought the truck in the garage today and the u joints are solid but the drive shaft has up and down play at the boot. not something that was noticable when i replaced the u joint. is the driveshaft no good? or is there a bearing inside that can be replaced?