Terrible Noise In Ls430 Worsening And Still Unsolved After 18 Months

[Ancdmd]

I have a noise in my '02 LS430 that has been there for 18 months and I can't figure out what is causing it. I've had at least ten mechanics at different shops try to diagnose it and they either can't hear it, hear it but don't know what it is, or have misdiagnosed it.

It started out as a tinny metallic rattling sound that I could hear above 60mph only when the car was coasting with my foot just slightly touching the throttle, but not enough to keep the speed constant. Now it has progressed to the point where I can hear a rattle constantly, although it is faint at lower speeds. It is quite noisy on the highway when coasting now. I can hear a rattle slightly at idle when parked, and it seems to be more audible around 2000 rpm.

The car has 137k miles and has always had all service. I've replaced the motor and trans mounts, and I just replaced the exhaust y-pipe and all rubber exhaust mounts. I had the forward cats and the resonator inspected and they are ok. I also had the driveshaft center bearing replaced and the shaft inspected. The only time I noticed a difference in the noise was when I had the motor mounts replaced, it seemed to be gone for a month but then returned. I've had the entire front suspension replaced at 110k miles and had it checked multiple times to no avail.

I can't be the only one who has ever had this problem! Any ideas? Video clip of sound below, it chimes in about halfway through:

[landar]

Thats going to be a tough one to solve. But if it went away for a month or so when you replaced the motor mounts, why don't you inspect the mounts again? Maybe something in that area has loosened up or a new mount is now broken (defective...it happens).

[1990LS400]

Your description of the noise sounds like one I had from a failing catalytic converter. How did they check the cats? Remove and shake them?

[Ancdmd]

The two forward cats were visually inspected when I had the y-pipe and rear cat assembly replaced last month.

[steve2006]

Common on the earlier LS400s was the exhaust heatshields rattling due to rusted broken fixings or rusted out bolts causing them to drop onto the rear mufflers so I guess the same could happen on the later LS430s.

If the fault is now present constanly that should help with diagnosis, grab an automotive stethescope for a few $$ and have a good listen around.