Just recently installed a lucky8 front drive shaft, then took the disco down a 40 mile road that hasn't been smoothed in about 50 years to get to some blm land to go wheeling and clay shooting. After getting back into town I'm noticing that there is a slight vibration, almost more like a humming sound, that seems to be coming from my drivetrain at speeds over 45mph while under load. While coasting or going slower the vibration either isn't there or isn't noticeable. It's a similar sound to my MT tires, it almost sounds like another set of MTs humming more quietly in the background. Should I be worried?

 

I'd check for out put flange play, but that is a classic bad u joint or loose shaft characteristic. Did you grease it up, good, before install? Are all your nuts and bolts good and tight? Did you use new nylocks on install? They can wobble loose if not

 

I greased it up really well and used the supplied nylock nuts. I may crawl back under tomorrow and make sure nothing worked itself loose though. As I'm sure you all know it's an awkward angle and can be kind of hard to tell exactly how hard you've got everything torqued down. Pretty sure they were all fairly tight but it was a really rough road so if anything was going to come loose this would have done it. Are the rear driveshafts prone to failure like the front shafts are?

 

All drive shafts are prone to failure. The front has an opportunity to cause expensive damage if it breaks. That is the fear factor that prompts all of the "fix that d.s....or else" mumbo jumbo. uj is rear uj. It goes bad and vibrates or breaks. Save the opportunity to pole vault,
No biggy. The rotoflex can be tricky because it can hide cracks and look ok, but still vibrate. I would def. check all is tight. My money is on loose bolt... And I plan to hit the mega million lotto, tonight.