Funny klonking sound from rear of car - not normal transmission noise

[fastlady]

Just wondered if anyone might have an idea what might be causing a klonking sound from the rear of the car when pootling along at steady pace along a road? Car is a 2002 S3 de-dion K roadsport, if that helps.

 

It's not the usual diff klonk as I'm getting that as well - it's an extra noise, which I'm sure never used to be there, higher pitched and more like the sound of something shifting from side to side and tapping another object, a sort of "tick-tick, tick, tick-tick" - not a regular "ticking" sound like a clock though but sounds as if something were rattling around in the car somewhere. But I've checked for the obvious things like something loose inside the cockpit or boot and can't see anything that could cause it, and it doesn't sound quite as random as that probably would anyway.

 

It also seems to be commensurate with the motion of the car and gets worse on rough roads as the car jinks around more, though it does go away altogether on occasions (interestingly under acceleration when the other diff klonk goes away, though that may be coincidence).

 

Any ideas? Is it just another type of diff noise I've not noticed before or something I should get checked out? I'm fairly sure it hasn't been there all the time I've owned the car and has only started recently (last summer, didn't drive the car over winter but still there on Wight Blat).

 

[Kevsta]

I have a similar one that has been there for a few years, I got bored of trying to trace it.

 

One thing depending on how thick it sounds (as in the piece that is making the sound - sheet metal compared to dedion tube?), if it sounds 'thin' then maybe have a look at the fuel filler cover plate, or the ali honeycomb floor. Others could be A frame, or worse still, fracture dedion tube

[fastlady]

Kevsta - thanks for that, and it definitely sounds "thin" (like that terminology!) like a piece of sheet metal, so hopefully that's a good sign! 😬

 

Will have a look at the things you suggest to see if I can spot anything obvious, plus I will get the de-dion checked out anyway as it's due a service in the next few weeks.

[charlie_pank]

Hmm, there's lots of stuff you can do to try and track it down:

 

1. Does it happen if you drive along at a constant speed?

2. Does it happen under acceleration?

3. Does it happen under deceleration in gear?

4. Does it happen under deceleration with the clutch dropped?

5. Does it happen under deceleration in neutral?

6. Does it happen under braking?

7. Do the noises coincide with the road surface - if you go over a pothole do you get the sound more?

8. If you put the car up on stands can you move the a-frame or the DD tube to recreate the sound?

9. Check the DD tube for cracks, especially at the mounting points for the suspension

10. Check that the diff mounting bolts are all still in place and tight

11. Check that the propshaft flange bolts are still in place and tight

12. Check that nothing is fouling the propshaft

13. Check there's no (more than usual) play in the a-frame and all the bushes are intact.

14. Does it happen when you turn one wheel by hand?

15. Does it happen more on left/right-handers?

16. Do the noises speed-up or slow down with the engine?

17. Do the noises speed-up or slow down with the road-speed?

 

back here because I want to be.

 

Edited by - charlie_pank on 21 Apr 2010 12:55:57

[malcolm1sim]

Watts linkage?

[andy_h]

Do you have a rear anti roll bar fitted, and has one of the drop links (arms) come off and is moving around based upon the motion of the car and 'tapping' it's surroundings?

 

 

White road legal 2.0 HPC VX race car - Now all shiney and new 😬

[fastlady]

Hmm, thanks all - lots of things to check there! 😬

 

Charlie - from your list:

 

1. Does it happen if you drive along at a constant speed? Yes

2. Does it happen under acceleration? No - pretty sure it doesn't

 

3. Does it happen under deceleration in gear? Do you mean deceleration under engine braking not whilst pressing the brake pedal?

 

7. Do the noises coincide with the road surface - if you go over a pothole do you get the sound more? Seems to though not it's not an exact correspondance with the road surface, it's similar to the usual diff noise in that as the car jinks from side to side on a rough road I hear the noise more, if I'm on a smooth road I get it less

 

Will try the other checks when I next get a chance to drive the car and let you know the results.

 

Andy_h - yes I do have a rear ARB (which definitely used to be connected!) and will check that out along with Charlie's list next time I get a chance - probably this weekend.

[Jason Plato]

I've had fuel linesn handbrake cables and wires rattling against the tank and chassis.

 

worth having a good look under the car behind the bulkhead and forward of the tank for any cgafing or loose things

 

one other strong possible cause could be a broken baffle inside the petrol tank. These do occur and do rattle as you describe. bit of a pain to get inside the tank so I would eliminate others first.

 

 

here is my Duratec R .... C7 TOP

Taffia AO

 

Edited by - Dave J on 21 Apr 2010 13:45:01

[charlie_pank]

Yes. I mean does it happen when you lift off the accelerator, but don't press the brake?

 

You mention side-to side motion, that might be a clue.

 

See what you can figure out about the nature of the problem from the answers you get to my questions...

 

back here because I want to be.

[GPBox]

I traced a similar sounds on mine to a front (yes it sounded like coming from the rear !)...brake pad tapping as the disk rotated...as soon as I put the slightest pressure on the brake peddle the tapping stopped......

 

worth a try

 

Graham

[metal mickey]

check for play in the inboard drive shaft joints. These give a clunk similar to take up in the diff on deceleration and sharp acceleration. Jack the rear of the car up and get someone to turn a road wheel while you check for play in the joints.

[Ian B]

Try popping off the centre caps of the wheels and see whether the half shaft domed metal cover has come loose and is rattling around inside the centre of the wheel behind the centre cap.

 

 

ETA: tends to make more of a 'tinkling' sound rather than a knocking, but if there's a lot of grease in there I guess it could sound 'klonky'

 

---

Ian - Slightly Vider SVelte SuperVeloce model 😬 - Joint AR for North Kent - Area details and calendar here

 

Edited by - Ian B on 22 Apr 2010 22:23:41

[Grubbster]

Thump the underside of the fuel tank and see if anything is loose inside. My baffle has fallen off and makes a rattling noise ☹️

 

Solent Se7ens Web!

[CageyH]

Also check the shock absorber lower mounting bolts are still in one piece, and not two!

 

 

Only dead fish go with the flow....!