[Dead Parrot]

It is possible that all of your power testing of engine and transmission could have moved a u-joint from the needs replacing in a couple of years category to needs replacing soon. It is also possible that since you are now listening to your truck closely, you noticed a noise it has been making for years. I had a drive shaft that made the tingy-clunk noise for years before the drive shaft started vibrating due to bad u-joint. Still clunks once in a while during a R-D switch due to a 40 year old drive train on its 3rd set of 100,000 miles.