driveshaft q

so i was reading thru my haynes and it says when your disconnecting hte driveshaft at a ujoint that you should mark it and put it back in exactly the same for balancing issues. is this true and what if you do an axle swap? I'm getting a whiring noise from somewhere in the back its been there since the swap but I don't think its the axle. any body got .02 I can borrow?

A whine usually indicates that the gear setup is out of specs. Does it whine on acceleration or coast?

While I was taught to mark u-joints, and still do it, I don't believe it is critical and it isn't applicable in an axle swap. However, after an axle swap, if a vibration is present it can sometimes be eliminated or reduced by changing the position.

If you have ever toured an auto assembly plant you would see that the only consideration given to the driveshaft, which was manufactured somewhere else and balanced without consideration to any transmission/transfer case/differential, is if it fits the vehicle's build spec that is currently coming down the assembly line.

That said, I mark flywheels, flexplates, brake rotors and drums, and yes the driveshaft and differential yokes too.