Patrol Front Wheel Vibration

This question i guess is mainly for past and present patrol owners. I drive a 91 LWB Patrol and on my recent easter trip whilst crusin down the highway doing about 100-110k/h the front right wheel started to vibrate / throw sideways almost as if it was about to break off. This happened a total of three times in the space of about 60k's and each time appeared to be set of by minor bumps in the road. The tyre was balanced recently and theres no other regular vibrations that one would associate with an unbalanced wheel nor does there appear to be any bumps on the tyre. This is the second time that its happend, the first time was after doing some brief low range 4wd, after which i took it upto 100k/h (in 2H) when the vibrations set in, when i checked the hubs one was unlocked, presumambly whilst doing 4wding in woody area full of little branches sticking in the way, anyway at the time i thought that onw hub being unlocked was the cause of the problem and since it didn't occur again before i got home i thought nothing of it again, coincidentally that was on the easter trip a year ago. I had a similar problem on a earlier 88 model SWB patrol and that time it turned out to be a crack in the chassis rail in line with the wheel. Naturally i've checked for the same thing happening to my present car but see no sign whatsoever. I am curious if others have had similar problems or if its just my lucky misfortunes. Thanks.