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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > Suspension | Chassis | Brakes > Suspension noise - crunch type sound.
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      08-19-2018, 04:56 PM   #1
adpack82
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Suspension noise - crunch type sound.

Can anyone shed some light on an issue I'm having?

Picked up my 'approved used' 2014 f30 330d, last month. It has 22000 miles on the clock and Its been back in to the dealer twice already, for the same issue.

The car was making a knocking sound over bumps, and a crunching noise, similar to the sound of scraping the undertray off the ground (its definitely not this), crossed with standing on a Coke can. The crunch happens on certain types of undulations, usually mid corner. Sounds like it's bottoming out, but it's not.

The car has adaptive dampers, which have had their software updated. Its also had a new wheel bearing, and both top mounts replaced, as well as 2 new tyres. (so much for approved used "multi pount check by expert technicians, on every approved used BMW" BLA BLA BLA)

The knocking has now gone, and it drives like a different car, with much better turn in and feel. However, the crunching noise is still there. It's very occasional, hard to replicate, making diagnosis difficult. It sounds like it's coming from the o/s front, although I think the rear might be doing it too, but I'm not 100%. (no fault codes on dampers)

It's not the anti roll bar bushes; I've been assured of this by the master tech, and I'm inclined to agree, as I had that problem on a Saab once, years ago.

Any thoughts, as it's driving me mad?

Last edited by adpack82; 08-19-2018 at 05:03 PM..
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      08-19-2018, 05:13 PM   #2
rak299
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Might be the front shock on the side you are turning toward
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      08-19-2018, 05:33 PM   #3
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Quote:
Originally Posted by rak299 View Post
Might be the front shock on the side you are turning toward
It's booked on Friday, so I'll ask them but I'm sure they checked last time. No faults codes either.
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      08-19-2018, 06:30 PM   #4
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set adaptive to comfort mode when they test - more travel
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      08-19-2018, 06:30 PM   #5
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Does the sound have symptoms of metal over metal?
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      08-19-2018, 07:42 PM   #6
adpack82
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Quote:
Originally Posted by cfm56d7b View Post
Does the sound have symptoms of metal over metal?
Nah, not really. Why, what you thinking?
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      08-19-2018, 07:50 PM   #7
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Aftermarket camber plates can be noisy but I suspect your vehicle doesn't have them. The occasional nature of the symptom might be related to the improper spring installation. The spring is probably subjected to rotation and at some point twists as the pressure builds and then releases.
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      08-19-2018, 07:53 PM   #8
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Make sure you don't have any rocks or pebbles stuck between the brake dust shields and rotors.
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      08-20-2018, 03:57 AM   #9
adpack82
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Quote:
Originally Posted by cfm56d7b View Post
Aftermarket camber plates can be noisy but I suspect your vehicle doesn't have them. The occasional nature of the symptom might be related to the improper spring installation. The spring is probably subjected to rotation and at some point twists as the pressure builds and then releases.
As I've just had new top mounts, it seems unlikely my springs have been installed incorrectly, twice!
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      08-20-2018, 03:59 AM   #10
adpack82
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Quote:
Originally Posted by Tag View Post
Make sure you don't have any rocks or pebbles stuck between the brake dust shields and rotors.
No, not the right sort of noise.
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      08-23-2018, 12:29 PM   #11
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No one else got any thoughts?
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      08-23-2018, 02:20 PM   #12
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Since you said mid corner, how about steering rack? Ask them to check if there is play in there. Mine will be changed next week. It makes kind of crunchy sound in certain situations if there is a small bump mid corner. Not like scraping though.
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      08-24-2018, 10:24 AM   #13
adpack82
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Quote:
Originally Posted by zeikei View Post
Since you said mid corner, how about steering rack? Ask them to check if there is play in there. Mine will be changed next week. It makes kind of crunchy sound in certain situations if there is a small bump mid corner. Not like scraping though.
It's more crunch than scrape, hard sound to describe.

I will put it to them, when it goes in on Monday. Do you have any other symptoms with your steering rack?
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      08-24-2018, 11:31 AM   #14
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The most obvious symptom for me is a loud rattle if you drive on a dirt road with washboard type of surface, even when going straight. In that case you also feel it thru steering wheel. No sound whatsoever when going straight over single speed bumps or similar. Steering feels usually fine but sometimes a bit notchy when turning left at low speeds like parking. My indy BMW mechanic suspected steering rack immediately when heard the symptoms and said it has a lot of play. Fortunately I don't have to pay for it...
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      08-25-2018, 01:44 AM   #15
adpack82
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Quote:
Originally Posted by zeikei View Post
The most obvious symptom for me is a loud rattle if you drive on a dirt road with washboard type of surface, even when going straight. In that case you also feel it thru steering wheel. No sound whatsoever when going straight over single speed bumps or similar. Steering feels usually fine but sometimes a bit notchy when turning left at low speeds like parking. My indy BMW mechanic suspected steering rack immediately when heard the symptoms and said it has a lot of play. Fortunately I don't have to pay for it...
I don't get any rattling/knocking over speed bumps either, (replacing the top mounts cured that one)The notchy steering I get on occasion. If I'm cornering hard left and hit bumps, mid corner, with the front right tyre loaded, that's when I get the knock/crunch sound. Sometimes more knock than crunch, sometimes more crunch.

I suspect it is the steering rack, arb bushings or maybe a CV joint. I'm assuming BMW checked the other bushings when it got its top mounts, but you never know.

I found a road last night, near the dealer, where I can reliably replicate the sound. Whatever is causing it, the car is under warranty, so I'll not have to pay either.
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