Well, I have good news and bad news for you. You were probably reading about my car. I was just logging on to write an update on this problem. And yes, this can be a really spooky condition.
I had this same thing happen to my '96 GS with 85K on it. The Toyota dealer was stumped. I took it to Lexus. They had no less than 5 technicians, including their chief diagnostic guy pour over it for about a week. What they finally came up with was this:
1) Bad wheels bearings on the passenger side, rear.
2) Bad bushings on the driver's side #1 control arm (vertical one)
3) Bushing on the rear cradle that isolate the the cradle from the body were deteriorating.
It took them another week to get the parts, then they had to remove practically the entire rear suspension to replace the bushings. The total for parts and labor was over $2K. They knocked 10% off the bill for me since it took them so long to figure it out.
I just got the car back at the end of last week. The problem was fixed. My car is in great shape other than this issue, so it was worth it to fix it. I plan to keep the car for a couple more years. If the rest of your car is not so great, then you have a judgement call to make.
I would recommend that you do fix it right away, as this tends to get worse and can ruin other parts. I would probably have them check the #1 control arm first to see if that corrects the poblem and then go from there. Maybe you'll get lucky and not have to replace as much as I did.
Good luck!
Thank you very much for the suggestion, I really appreciate it. I did take it back by the dealer but unfortunately I didn't read your comment until AFTER I got it back. However, I think what I may do is write Lexus because personally I feel that the Service Department kind of blew me off and figured I was some 'goofball'. I've been bragging about Lexus products and their service and I was kind of disappointed at how they treated me when I picked the car up.
Thanks again for your comments.