Tire noise from rear end, Solved, mostly

[gwgang]

Update 2:06/19/2016

I had spoke too soon.  The noise is much muted, and it happens at a steeper steering angle(left turn to 9:30 position).  Thankfully such turns are rare on the interstate.  Next step: lubricate the bushings with silicon grease.

Original post:

I had a curious problem couldn't be solved by my indy mechanic and my Lexus dealer.

When turning left at highway speed(above 40 mph), I will hear noise, like going over uneven surface.  Sounds like, plop, plop, plop.  The sound only occur when the steering wheel is between 12 to 10:30 position.  Any steeper to the left, it disappears.  Also, the plop sound is not really continuous.  On a sweeping turn on interstate, it may go on 3 to six plops, skip a beat, then continues.   It sounds like coming from the rear left.  It happens either coasting or accelerating.

I had a similar noise two years ago, but it happened when I turned right.  My Indy mechanic traced it to my rear left lower control arm, which is cracked due to rust from impact with road debris.  He replaced it, and it went away.

This time, my Indy mechanic fail to trace the problem.  He initially id the leaking front struts as the problem, but replacing front struts and control arm bushings didn't solve the problem.  He later rechecked, and told me that the loose bushings at the rear knuckles may be the problem.  Since replacement cause more then $1200, and he told me it's not a safety concern, I let it rest. 

Two months later, I went to Lexus dealer for a check engine light and VSC Anti-lock brake warning light.  I told then to also diagnose the noise since I was there.  They checked, and told me I need steering angle sensor calibration.  $400, and they didn't fixed it.  I went back two days later, and did a test drive with a Lexus mechanic.  He said he heard whining noise from CVT bearing, notice steering vibration at 20 mph turning either way, and feels the ploping noise may be due to faulty front differential.   Back at the shop, they diagnosed the suv again,  and told me a bearing is failing in CVT, front and side engine mounts are bad, left front drive shaft, front lower control arm, and left front strut are bad. 

I am not convinced they made the right diagnosis.   Noise comes from rear left, and only really noticeable when turning left.  Sure I heard the ploping sound at lower speed on local streets going either way, but that's more due to uneven pavement.

About that check engine light, dealership also did a half baked job.  It was code p0141, p0147.  Fuel trim engine lean.  They replaced exhaust manifold gasket, exhaust pipe gaskets, cost $1000.  7 days later, CEL returned, same code.  Since I lost confident in dealership's competency, I went to my indy mechanic for spark plug change and had him look into it.  He found one of the intake hose near air cleaner is leaking, and wrap tape around it to fix it.  At this point, I bought a bluetooth OBD2 reader and OBD car doctor pro.  The readout confirmed that my long term fuel trim returned to normal at 3%.  It was 25% before.

After spark plug change and the fix, my mpg went from 21 to 24.5, but hot weather and traffic congestion kick it down to 22.5mpg again.  Anyone looked at the long term fuel trim lately?

 

Update 1: 06/12/2016

Noise is gone!

Just got my rear struts, strut mount and boots replaced 3 days ago.  The noise is gone.  I drove through a stretch of highway that always generate the noise before, and the continuous bumping  noise is gone.  Only single tire bumping noise now, and I could blame it on occasional uneven pavement.  So my old struts were not doing their job; spring is bouncing up and down and slapping my tire to the ground. 

With the new struts, my ride is still a little too firm for my taste, and cabin noise is only slightly muted than before.

btw, my local mechanic didn't change my front strut mounts and boot when he changed my front struts a few months before.  He was trying to save me some money because he knows my wife doesn't want me to spend too much money on repair.  In this instance, he should have called me because I definitely want them changed.

Side note:  That whining noise Lexus mechanic hear?  I heard it when I was recharging the A/C refrigerant R134A.  I think it's the A/C Compressor because it whines when the A/C cycles on.

 

Lessons learned: 1.  Don't rush to Dealership for repair when you are in panic mode.  Had your trusted local mechanic check it out first.  2.  Mechanics make mistakes too, they are only human.  3. When Check Engine light went on, a Toyota car may decided to turn on VSC and Anti-Lock light too, according to my mechanic.  4.  Your strut is a wear component, it degrades gradually; Oil leak from strut or bumper bouncing up and down are not the first signs of degraded struts.  Struts don't last 100,000 mile on a heavy car or SUV.

Edited June 19, 2016 by gwgang
update

[RX400h]

May I ask how many miles are on your odometer? Ours has approximately 102,000 miles and has never had any of the issues you mentioned.

[gwgang]

My RX400h had 120,000 miles on her.  I don't drive it fast, but every 2 to 3 weeks, I had to load some heavy stuff on it for 40 to 60 miles.  I didn't know RX400h's load capacity (about 900 lbs) before, but now I realized I over loaded it by 300 lbs.  Also, my daily commute include some NYC's broken pavement local streets. 

I will be replacing the rear struts in two weeks because the struts are not doing their job handling the small up and downs of broken pavement.

I just drove over some freshly paved highway last week, and there are no interruptions between the ploping sound as I mentioned earlier.  So I was wrong about that.

 

I will report back when I get the struts replaced and see if there is any improvement.

[RX400h]

I remember those East Coast roads well. Please let us know how the strut replacement works out.

[gwgang]

Updated the original post after strut replacement.

I bought the KYB Excel-G struts, mounts and boots from partsgeek.com because their shipping charge is lower than Rockauto.com.