Driveline Vibrations - not sure if its a vibration or hum

I have been reading about the vibrations that folks have been having on their 2nd gens and the multitude of causes and fixes.

What I am not sure of though is if mine experience can be described as a hum and not a vibration - I guess it depends on how severe it is I guess.

Thing is, my dcsb is stock suspension with the exception of aftermarket rear springs to replace the cracked ones. They definitely sit higher in the back end than before and the garage that changed them out said it will settle in after awhile.

Anyway, I was cruising down the highway around 65 mph and I could hear more than I could feel a hum coming from the drivetrain. If I let off the gas or speed up a little it would go away, but once I hit the cruising speed again, it would be like a dull hum. Its kinda weird cause I could "feel" it but it wasn't so much as to call it a vibration.

Before I start digging into this (CB flip/drop, axle shims etc etc), I just want to ensure that I am on the same page as others.

 

After driving for a while, slide under there and see if the u-joints are hotter than the surrounding drive shaft.
Recently I had a noise/hum, but no vibration and the sound frequency of which changed with speed...that turned out to be front wheel bearings.