...been in the shop 4? times and the mechanics have heard it too but they now tell me I need to duplicate the noise. They have replaced the manifold (it had a crack) the O2 sensor was melted to something. Then they thought they had to replace the CAM but after opening it up realized it had the new parts. Now they tell me to duplicate it and there is no safety concern. I duplicated it this morning now I have to take it back in. Any suggestions? Has anyone else had these problems. It only has 35,000 miles on it, I bought it certified used through Toyota 5 months ago and have only put 5,000 miles on it.