2011 E70 35D Strange sound when decelerating

[andrewwynn]

Important detail of guibo install

https://youtu.be/Vw7Zbp1rfGI

[One365thIrish]

Originally Posted by andrewwynn

Take a listen to a loose guibo bolt situation. Was yours taken apart and reinstalled? It's important to get the bolts the correct way and some use washers also critical.

Reused bolts can also throw off torque application and have the bolts not be tight enough.

It's possible the sound is a shield getting hit by a rotating part that only happens from flex under engine braking. Look for things that are close to the drive shafts and telltale rub.

In the beginning of the video there is a very repetitive sound. Like tap tap pause tap tap pause.

Loose shields and/or panels was my very first thought since I had removed most of them to install the new downpipe and mid pipe. Nothing had rub marks and and pieces were clear from moving parts.
I had to use my 1/2" breaker bar with some "umph" to loosen the guibo bolts and the guibo was was facing the right way with the bolts placed properly.
I did find 1 motor mount bolt not seated all the way and I can't specifically remember torquing the subframe bolts when I buttoned everything back up.
Of note, I live down a 1/4 mile gravel road and it doesn't make the noise on it.
So my replacement ATC700 will be here Friday, I'll get everything back together and test drive with the gopro mounted in various locations and go from there.
Thanks for all your input and links Andrew.

[andrewwynn]

100% chance to track this down. XO rarely ever fails.


Sent from my iPhone using Tapatalk Pro

[One365thIrish]

Alright, got everything put back together and torqued to spec, the subframe was already torqued from dpf delete. Still getting strange sound, but I noticed that the engine has to be warmed up for it to happen and the RPM fluctuates with the noise. I shot video from various spots around the engine to try to pinpoint the origin.
https://www.dropbox.com/s/jrod2nyoq0...sound.mp4?dl=0
When I did the delete I replaced the thermostat and also did a swirl flap delete.
I'm still learning how to data log with my Foxwell NT510.

[andrewwynn]

That is one of the craziest things I’ve ever heard. You need to use an app like FFT to figure out where the sound is coming from because it will measure not only in the sound pressure level but all the frequencies related. You can definitely figure out for example is it coming from the left or the right of the front or the back.

Also use the vibration app determine the exact frequency of those clicks you can also just use an app audacity To look at the way for him and measure the milliseconds between those clicks.

We can determine from the speed of the car where are the sound is coming from based on the revolution in the drivetrain.

Is it possible that some thing controlling the turbo wastegate or boost Is somehow clicking open and close.

Perseverance is going to pay I promise. It’s way too obvious in way to repeatable that we can’t find the problem

[13brian]

Agree with andrewwynn, that is really quite something. Definitely not a pinion bearing issue, now that I hear it. The tapping, at first, sounds somewhat like a spark arcing or exhaust leak tap. Listening to the video (at watching what little can be seen) does not lead me to believe it is RPM related, unless it is in combination with speed and flex from acceleration /deceleration. It seems most to me like exhaust tap, as above could be turbo related possible EGR. Quite loud to be an internal noise, leaning towards leak somewhere. Curious indeed, quite frustrating I am sure.

[andrewwynn]

Need to determine if the sound is in sync with the engine or drive train.

I'm thinking that is a rotating part contacting a heat shield.

Imagine a bolt from flex disc but just two of six hitting;

Tap tap pause pause pause pause tap tap then after a while three hit so it's tap tap tap pause pause pause.

The engine braking just putting torque on the motor to move things around.

Check the mechanical fan of your engine has one. I've seen it happen when engine torque moved the fan enough to contact the shroud and the sound of each blade slightly hitting the shroud was similar. (though this sounds more metallic)

[One365thIrish]

Thank you andrewwynn and 13brian for your input.


Here's where I'm at so far:
The sound appears to be coming from the passenger side front near turbo
No mechanical fan
Happens at all speeds and RPMs

No DTC's or CEL's
It doesn't happen until engine is warm
Only happens when decelerating and goes away with slight acceleration
Not the waste gate
Not the transfer case or drive line

Didn't have this sound before EGR, swirl flap, def, dpf delete with 2.5 tune and VRSF downpipe. I replaced the thermostat as a prevention.
Other than the noise, it runs great. Drove 40 miles last week and just 2 footed it.
Going to do vacuum testing next week. I already replaced most of the vacuum lines last week.
Really stumped.

[andrewwynn]

A couple thoughts:


1) vs. a little throttle, does putting in neutral stop the sound

2) it's reminding me of Jake brake just intemittent and softer and higher frequency than a semi.

Does your engine have exhaust braking? I could not find reference yes/no online.

3) intelligent alternator control; the alternator is supposed to charge "only when braking/coasting"; if the alternator is kicking on/off a surge of force related to this could be causing motion that is causing right a physical tap or a surge of current can cause wires to slap.

[One365thIrish]

Originally Posted by andrewwynn

A couple thoughts:

Putting it in neutral does make the sound go away. (Just tried it.)
No exhaust brake.
Turning DSC off/on makes no difference.
Not sure about the alternator. No spikes shown on the Foxwell.