Light knocking noise from the chassis

[TANKSLAPPER]

I would appreciate your help.

I’ve got a light knocking noise which seems to come from the front end of the car, only when it has warmed up, the hotter it gets or the longer the run the noise is louder.

I can only hear the knocking when the car is freewheeling and slowing down in a straight line from about 35mph to 5mph ie with no load

The parts I have changed to try and rectify this problem are:-

Front suspension and top mounts
Front lower wishbone and rose joints
Front lower wishbone bushes
Engine and gearbox mounts
Rear trailing arm bushes with limiter kit
Exhaust mounting rubbers
Anti Roll bar drop links

The only other things I can think of changing is the steering rack , or the rear camber arms

[SMD]

Prop Shaft?

[NZ_M3]

Describe the noise more .... i.e. is it a clanking sound? or metalic sort of a knock or a dull thud thud thud ...

It'll be a rotational related - so work from the wheels back and check every component from there on.

Given that it's not a load related noise you can rule out engine mounts and gearbox mounts.

Might be a wheel bearing, but these seem to rumble rather than knock.

[TANKSLAPPER]

Describe the noise more .... i.e. is it a clanking sound? or metalic sort of a knock or a dull thud thud thud ...



Thanks for your response, I don't think it is the wheel bearing as this is a problem I have had for the past 30 months, and have traveled some 20,000 + miles since it occured

The sound is mainly heard around 20 mile an hour and it is more of a bobbling/bouncing dull knocking noise, and you can feel it on the near side when free wheeling

[NZ_M3]

Check your tyres ... sounds like there's a flat spot on one of the tyres.

[TANKSLAPPER]

Check your tyres ... sounds like there's a flat spot on one of the tyres.

No its not that, I had four set of tyres since the noise begun

[Steve Gill]

Any chance you could record the noise on your mobile phone and post it? Might give us a better idea.

[bryce]

The sound is mainly heard around 20 mile an hour and it is more of a bobbling/bouncing dull knocking noise, and you can feel it on the near side when free wheeling


Does it do it if the car is out of gear? are you familiar with the knocking noise you get with SMG at lower speeds?

Video / sound clip would be good buts its always hard to capture these noises. :banghead:

[TANKSLAPPER]

Any chance you could record the noise on your mobile phone and post it? Might give us a better idea.

Hi, I can just see me hanging the missus out the side window by her legs whilst recoding the noise. LOL Nice one

Unfortunately the noise isn't to loud and it only does it for a 5 to 10 seconds

Simon Hill reckon it could be the brake pads

Thinking back, it was the time I fitted the ap's on.

I jacked the car up today and when I turn the wheels back and forth you hear a light clonking noise. Also the calipers being aluminum they would expand more as they became hotter.

I will go out later for a test drive and see if the noise stops when I brake.

[bryce]

Simon Hill reckon it could be the brake pads

Thinking back, it was the time I fitted the ap's on.

Think Simons got it for you... Mark_CSL's car does this too cos he's got floating calipers on the rear (not APs, but bigger ones).

He'll be along shortly Im sure...

[TANKSLAPPER]

Hi Bryce

I am familiar with the knocking noise you get with SMG at lower speeds, It's definitely not that.

Thanks anyway

[TANKSLAPPER]

Finally think I have found the noise with help of ETA motorsport at Brands Hatch
They reckon it is coming from the right hand drive shaft inside the rear diff
We changed the diff oil and the noise is slightly less now.

This fits the description I gave:-
“light knocking noise, only when it has warmed up, the hotter it gets or the longer the run the noise is louder.
I can only hear the knocking when the car is freewheeling and slowing down in a straight line from about 35mph to 5mph ie with no load”

So I need a new diff and drive shafts, has anybody got a view on how I should go about it.

ie. Try my luck with BMW for a good will warranty claim, Reconditioned, new, change the final drive ratio’s,

And does any one know the likely cost ?

[Mark CSL]

Try bmw for a good will or buy a warranty and then discover the noise :hahaha:

[derek]

Hi i got a new diff last month i think it was £1800+vat+fitting, its was covered with the warranty, car is so much quieter and no clonking at slow speeds with no drive

[lfc]

Almost certainly the pads running extra feely in the calipers. Its no problem but an annoying noise. It happened to me on my M6 when I fitted Brembos. Look on the bright sde - less drag!

[bryce]

I get these symtoms too tankslapper. You think you'll get a new diff?

Derek, what was your symtoms and many miles your car got?

[derek]

I get these symtoms too tankslapper. You think you'll get a new diff?

Derek, what was your symtoms and many miles your car got?


the car did clonk at little with no drive at low speed, there was found to be more movement on the diff than another m3 the garage compared it too, mileage was 38k, Big difference in the driving noise level and s6 changes

[TANKSLAPPER]

I finally solved the knocking noise.

The piston in the front suspension was knocking.

Remedy was to adjust the front coil overs up by 1mm

spend months trying to solve this, and it only took 5 min to sort it.

Now working as new.