As I mentioned in an earlier thread- it should be pretty easy to tell which end of the drivetrain the vibe is coming from because everything prior to the differential turns at least 4 times faster than after it, so the frequency is higher.
Same with fore/aft of the transmission, depending on what gear you are in.

You can eliminate a whole lot of things right off the bat that way, but its all pretty tough to do over the internet...


'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik