Driveline Vibration-5kSQ-Help???

[Jon Archibald <JArchibald@whpacific.com>]

Patient: '87 5kSQ, 161K miles

Symptoms: 
-Low pitched growl on launch (especially if launching into a turn)
-Low pitched hum/vibration while accelerating, especially between 2500-3000
rpm
-I can't pinpoint where the noise is coming from, but it seems to vibrrate
the length of the car
-symptoms cease when cruising (in gear, maintaining speed)

I have very little experience with driveshafts and/or vehicles with more
than one differential so I have no "feel" for troubleshooting in this area.
I think maybe the drive shaft is not properly aligned (the Bentley says
having it not properly positioned will cause noise and vibration). 
Any input on this subject is greatly appreciated
I am located in Portland Oregon.
Much Thanks in Advance

Jon