Just pulled both of the driveshafts for complete overhaul. After getting ready to pain them and install new u-joints, I noticed that there is something loose inside of the front driveshaft. Research revealed that there is sound deadening cardboard material inside, and when it comes loose it is nearly impossible to balance it. Here is the video of what it sounds like:
Loose sound deadening material inside front driveshaft - YouTube
Any thoughts on this from people who have experience with driveshafts?