I have a 2008 Lexus RX350 and it makes an intermittent rattling noise from the exhaust only when the car is warming up. I checked to see if there was something loose and there wasn't anything loose when I touched the exhaust when it was cold. I also don't hear an exhaust leak at all. I pinpointed the noise to the bottom of the car around the flange area near the resonator but I'm not 100% if its there.
I had a remanufactured engine installed at 143,000 miles and have put around 3500 miles since then. I checked for codes to see if it was possible one of the catalytic converters were going bad but everything looked fine, and I don't have a check engine light.
I also took two videos of the noise. The links is here
https://www.youtube.com/watch?v=7G_Y1zIz6o4
https://www.youtube.com/watch?v=omfTSOVN_uI
If I had to guess, I’d say it was one of the pulleys.
But try this tool to get some proof if you’re looking in the right area -
Also -
I do hear noise from the pulley area and I had recently had my mechanic replace both the belt and the idler pulleys. I’ve also in the last 20,000 miles replaced the alternator, power steering pump and water pump.
The noise does not go away
Then you’ll have to pinpoint the noise using Scotty’s technique in the first video above.
Your timing chain needs replacing, at 3500 miles. Who rebuilt your engine, Ray Charles?
Nope, it’s a Jasper remanufactured engine. Additionally I looked at the live data on my scan tool and didn’t see any misfires or cam timing problems. There is no engine rattle.