So I dropped off my IS250 for it's 5k Check and oil change and told them about a metal rattle that I heard. I only heard this rattle when I accelerated but only at a gradual acceleration. It didn't happen if I accelerated at a higher rate. I thought the sound was coming from the front of the car and sounded to me like maybe the clutch plate. (it sounded geeatly like two plates pinging together) After that he told me they'd look into it and I should have the car back today. I got a call today to find out the exhaust system was causing the rattle and they are replacing the whole system and mounting brackets. He didn't say what part of it was rattling but I just thought everyone might know about this noise. I don't drive my car hard at all and I have read arounf this forum about this noise before. People said it was the clutch and it was a normal noise. Be aware that this is not the clutch and could cause major problems down the line.

 

Thanks for posting this, I was suprised to hear the whole exhaust needed to be replaced. Nonetheless, warranty (LOL). Kind of sounded like a loose hangor.