Lexus RX 2010-15 :: Substantial Clunk Somewhere In The Rear

I've had my 2012 RX 350 for more than a year now. From the very beginning I had this occasional problem: Stopping fairly quickly (but NOT any sort of panic stop) at a small downhill, I sometimes would get a rather substantial clunk somewhere in the rear. It sounded pretty serious--axle or suspension, I thought. Of course when I first brought it to my dealer. I couldn't duplicate it. But then, I convinced the service manager to send a mechanic to my house, where there's a place where it often happens.

Finally, he heard the clunk . The service manager did some research and concluded I was hearing an "over-extension of the suspension". He sent another RX350 to my house, and indeed, we were able to replicate the clunk at the same place, in that different vehicle. On the other hand, a friend, who also has an RX350 said he never had the problem.

The service manager says there is nothing abnormal about the clunk. This is hard for me to believe. It's a really substantial clunk and in my 45 years of driving I've never experienced anything like it.