I have a 2004 base model Ls430. A few months ago, it started to make a humming noise in the cabin. It sounds to me like a poorly isolated moving part under the car is transmitting vibration onto a body panel. This cabin noise is directly related to the car's speed. It starts with a low hum at low speed, and as I go faster, the pitch goes higher and louder. No noise at all when the vehicle is at a stop even if I rev the engine. It’s also separate from road/tire noise. I can tell the change of road/tire noise when I go from blacktop to concrete pavement, but this this humming noise is superimposed on the road/tire noise and remain constant with the car’s speed. I tried taking a quick zig-zag while going 30mph, and going over bumps, and throwing the car in “Neutral”, the cabin noise remained constant.
Here are some of the work I’ve done to the car:
1. Took the car to Lexus dealer and was told that I had a bad front wheel hub. I decided to purchase the parts and replace both front wheel hubs myself. No change in the cabin noise. Note: I checked before the work, one wheel hub has a slight play and the other 3 were tight.
2. Took the car to another Lexus dealer and was told that all LS430 makes that noise, but later suggested that the motor mounts were bad. Again, I purchased all 3 mounts and did the work myself. No luck, the cabin noise persists.
At this point, I have very little confidence left in the dealer. Looking around on this forum, I found suggestions that the differential can be the culprit, and so I drained and refilled the fluid. The old fluid actually didn’t look too bad and I did not see any metal shavings on the magnetic plug. While the car was on jack stands, I put it in gear and try to locate any knocking or grinding sounds (put a large screw drive tip against the part and put my ear against the handle). Nothing unusual found. The fluid change did not get rid of the cabin noise.
I originally planned to replace the rear wheel hubs next, but with my track record so far, I’m probably replacing the wrong things again. Please help!

 

Sounds like a wheel bearing.

 

I know, I'm stating the obvious and what you have already said... But.... It's a rotating part somewhere, maybe a mount (transmission) However, I think it would be more of a clunk than a continual frequency noise.... Are you getting any unusual noises when shifting from natural to drive or reverse to drive while at a standstill?

If front hubs have replaced, I would seriously look at the rear. Could be a drive shaft U-Joint that's going dry. Stupid question - have you ruled out tires, as you rotate tires does anything change?

Has it gotten worse with time?

Now I’m really reaching, you don’t have a brake hanging up. How’s you MPG? How’s the emergency brake working? Wondering if maybe pulling the rear rotors to check the E-Brakes….

Just thinking out loud.... Keep us posted.

My RX330, I could have sworn I had a tire going bad, it was a front wheel bearing hub.
2001 LS 430 now has 178K on it,

 

could be the driveshaft center support bearing, mine failed and started whining, increased with road speed.

 

Check the gear selector gasket, you can see it from the bottom of the car, mine is completely torn, feel same noise like you.

 

Thank you all for several good suggestions. I checked the CV joints for leaks and torn boots this afternoon - Nope, they all look good. I will try the following as recommended this weekend and report back...
1. Rotate tires - test drive
2. Check gear selector gasket - visual inspection
3. Check drive shaft center support bearing - put car on jack stands and in gear, then listen with stethoscope.
4. Remove rear wheel hubs from car for inspection - I've tried the 6/12 O'clock and 3/9 O'clock rocking test already. Both seemed tight with no play.

Thanks again...

 

Mine is startng to wine from the back half of the LS. Does yours sounds like a bunch of crickets screaching around dusk? Anyone?

 

Tried the following to eliminate cabin noise. Unfortunately, none of them worked...https://www.clublexus.com/forums/ima...lies/Peace.gif
1. Had all 4 wheel balanced and rotated (tires are around 1 year old). Test drove the car and for the first 1-2 miles, the noise seemed to have significantly lessened. But after a few miles, the noise gradually returned. By the way, NTB guy suggested that the noise could be from a bad strut mount that's transferring vibration from the strut to the car's body.
2. Checked drive shaft center support by unbolting the bearing from the car. The rubber surrounding the bering looked good, and the bearing turned freely without making any noise.
3. Checked shifter gasket/seal from under vehicle. Used compressed air to spray from under the vehicle and tried to listen and feel for leaks into the cabin. None found!
4. Next weekend, I'll remove the rear wheel hubs from the car to check for noise. It's difficult to turn the rear hubs while they are attached to the drive shafts.
5. Thing to try in the future is to replace struts/mounts.
Any other ideas?

 

This could be a fuel pump that is slowly failing. We had a humming sound we couldn't find in our '04 UL and couldn't find it. The pump started failing a month later - making the engine quit.
We replaced the tank mounted fuel pump and the humming noise went away.

 

Have you checked wheel bearing?

 

Just because there is no play does not mean a bearing is still good. They start to whine usually as grime builds up. You really need to visually inspect the bearings to see if they are beginning to fail.

 

Mystery solved - it was a bad isolator. The rear strut/spring assembly has a rubber isolator on the bottom side of the strut mount. This isolates the coil spring from transferring any vibration to the cabin. One of my rubber isolator was rotted allowing the coil spring to come into contact with the strut mount. Once I replaced my rear struts with new isolator, the humming noise disappeared totally. Thank you all for contributing.

 

Not trying to prolong the agony of your pain, but aren't you FURIOUS that you replaced what the Lexus dealer "said" it was? You changed the hubs AND the motor mounts on their recommendations! Obviously they were NOT the cause of the problem and were not the fixes. Did you pay the dealership some sort of diagnosis fee for the time when they told you the hubs and the motor mounts?

I wonder what would have happened if you had THEM replace what they analyzed to be wrong, and the problem still existed? I wonder if they REALLY knew what the culprit was, but were giving you a jacked up estimate to replace the 'listed' parts, and never would have replaced them, but merely only replace the rubber isolator on the strut?

How much was the new isolator? How easy was it to fix once the issue was identified? Who found the problem?

 

No charge for the bad recommendations! Both Lexus dealers’ diagnosis came in the form of “free estimates”. The front wheel hub was a good call (one of the front hubs was bad), just not the one that causes the hum. Replacing the 2 engine mounts and the transmission mount did not do anything to cure the hum.

One of the things I tried, to eliminate the humming noise, was to have my tires balanced and rotated at NTB. I talked with the technician there about the noise, and he suggested that it could be caused by a bad strut mount. I decided to replace both sets of rear struts and mounts. Unfortunately, the KYB strut mounts I ordered did not come with new isolators. With my car torn apart on a Sunday, I cannot wait for mail-ordered isolators to come, so I picked up a pair of Monroe strut mounts/isolators ($42 each set) from a local auto parts store.

It was my first DIY on replacing the rear struts, and I did not find any step-by-step instructions for it. The first strut took me over 4 hours – mostly spent on trying to get the strut/spring assembly off of the car. Turns out if you separate the upper control arm ball joint from the axle carrier, you can create enough room to easily remove the strut/spring assembly. The second strut took about 30 minutes to remove.

I'd definitely credit the NTB technician for making the correct diagnosis.

 

It's nice reading how the solution was realized & implemented. I'm amazed the dealership didn't charge you a dime for their time, too! What a finale/ending to the saga!