Duke, sounds like a very similar issue. Mine didn't squeak, probably cause I greased the splines once years ago. Mine just had a little thumping vibe at driveshaft speed. I'll bet they are due to the same problem - the big nut not locking the splines down well enough. I could actually grab one end of the shaft tube and twist it back & forth by hand and hear/feel the splines click on each other. By the way, I found a big crescent wrench at Harbor Freight that just fits the 46mm nut.

DG