It's not engine pinging you are hearing. You already said you really hear it when you are coasting or barely pressing the gas right? Totally opposite of how cars demonstate pinging. Plus, our cars have knock sensors and can retard a lot of the timing preventing pre-detonation from low octane fuel. I think you are hearing gear or bearing whine. Is it constant in tone or rattle like metal against metal?

 

I agree it's not engine pinging or detonation. Yes I mostly hear it when very LIGHTLY coasting, which means my foot is actually touching the gas pedal but not enough to maintain a constant speed, which occurs frequently on the highway. I also hear the noise at other times though, sometimes when decelerating, or down/upshifting, and sometimes during some acceleration. I have ruled out just about every bearing and gear. I've never heard a bearing or gear sound like this, and after three+ years either of those would have resulted in something seriously malfunctioning.

The cat(s) are the likely culprit for several reasons. First, I checked and/or replaced a multitude of parts, so there's very few left. It's not something external that is banging around, I've checked every part under the car many times and everything is secure. Engine oil and trans fluid are clean. If one of the two cores is loose inside a cat, it could rattle depending on different frequencies of vibration in the exhaust flow, and vary depending on any slight change in the shape of the cat casing, which can result from minor flexing of the exhaust system under different loads and conditions. If a core is loose but not broken it won't leave pieces downstream in the exhaust, and I haven't found any when I replaced the y-pipe. Also, it likely won't throw a code since the exhaust still passes through the intact core structure within the cat. The area where the cats are is exactly where the noise sounds to be coming from, ruling out anything from the front seat rearward. The video I posted in this thread is the only clip I've heard where the sound and pattern of it's occurrence is EXACTLY the same as mine. Also, this noise appears to be extremely rare since no other members have reported it. A loose but intact cat core that doesn't throw a code is likely a very rare problem with the LS430.

The parts shipped today and I'll have em on the 30th, hopefully I can get them installed soon after and get to the bottom of this!

 

I have the same metal clinking sound. As you said, mine occurs when i tap the gas pedal and left off. To me it seems like some sort of linkage associated with the gas pedal, but I don't know for sure. It doesn't cause any problems, but it is annoying.

 

I just finished replacing the catalytic converters, amongst other things. Inspection of the original cats showed no problems that I could see, nothing was loose inside them and the cores were not clogged. The casings appeared fine. I debated putting them back on the car but though maybe something could be wrong internally that I couldn't see so I took a chance and installed the new Magnaflow cats I had purchased. During the removal of the originals a stud broke so it took 4 hours of wrangling to get the stud out. What a miserable job. I buttoned everything up and went home for the night, and sure enough the darn rattle was still present, along with a couple gasket leaks. Gambled and lost.

Back on the lift in the morning to fix the gasket leaks, I re-installed the y-pipe. Leaks fixed, but just didn't sound right, and I was determined to find this rattle. Put it back on the lift and noticed this area of the center pipe resting on a crossmember. In a eureka moment I thought I had found the rattle source. I used a transmission jack to raise the exhaust pipe and re-tightened the clamp, and the pipe then stayed up off the crossmember but was still close. I then used a couple exhaust clamps to support the rubber hangers further back, and a few washers to drop the crossmember a bit, providing ample clearance for the pipe to move around under varying driveline loads.

The rattle noise is definitely less frequent, but still occurs. I'm guessing some other area is rubbing up close to the motor, but couldn't find anything today. I'm kind of disappointed in the design of the center area of the exhaust, it appears that over time the exhaust sags at the joint between the y-pipe and resonator assembly and comes into contact with that crossmember. Grrrrr...

 

Did you save your old cats? You may need them again...

 

Yes I saved them. The Magnaflows have a stainless casing and a generous warranty so I doubt I'll still own the car when they do eventually fail, but nonetheless I have the original cats for backups. These stock cats fetch good money on the used market, I could even resell them and recoup most of my costs.

 

I had an issue on my LS400 with bad cats. OEM is very expensive. The shop replaced with wrong Magnaflow version and they only lasted 3 months before getting the old 420 & 430 back. But you probably got the right ones. I had them fix it but still. LS is bit sensitive on the cats.

You know, from your description of the sound it seems to me you are describing a whine not so much a rattle. A constant tone? Am I right?

 

No its not really constant at all. It's like a bunch of jingling keys on a keyring. Sometimes it sounds kind of constant and low volume, but overall the loudness and intensity of it varies greatly. Other times I'll be going quite slow, under 15 mph, and it will make a sudden short racket, like if you bumped your keys in the ignition with your knee. When this happens I think it coincides with an up or down shift and a cold transmission, or letting my foot off the gas. The inconsistency of the noise is making it a pain to diagnose. Whatever it is I believe it is something rubbing somewhere, as it is affected by the positional movement of the engine, driveline, and the vibrations/harmonics of the system at different loads and speeds.

 

The reason I ask is because I also hear a sound or tone sometimes when decelerating at highway speeds but mine is faint and can only be heard with the radio off and I'm listening for it. I just attributed it to gear whine or an exhaust note but the sound I hear is never a rattle. More of a low-mid whine or tone.