I week ago I bought my GX470. While I love the car I have run into one issue has has very quickly become a pain in the neck. After the first couple of hundered mile I start hearing a light knock underneath towards the back of the car. It started as a couple minutes apart but then grew to a regular knocking. It never affected the way the car drove. Speeds 30-70 mph it happens very regularly. Anyways I took the the car to the dealer. Just before I got there I had to make a sudden stop at a stop light and thats when I heard a loud metal snap in the back and the sound stopped coming. Of course the service guy took a test drive with me and never heard it. Turned the car in for the night. They looked at it , did not find anything. Guess what the sound is back again and again I hit the brakes and with the lod snap the sound is gone. Any clues.