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Mike
Mike, BMW Technician
Category: BMW
Satisfied Customers: 39198
Experience:  Tech Expert
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Hi Steve, I have just bought a second hand (08) BMW 118d SE

Customer Question

Hi Steve, I have just bought a second hand (08) BMW 118d SE 143 3 door on 39000 miles. On the way home from Dealer the following happened and continues to happen. Immediately when the rev counter falls below the 1 mark there is a knocking sound which appears to be coming from the dashboard. It stops IMMEDIATELY when rev counter goes above 1. It is almost as if there is something loose inside the dash however I doubt this is the cause as the noise starts/stops so precisely when rev counter is below/above 1. The noise can hardly be heard outside car with engine running and bonnet up. It can only be heard inside the car. It happens regardless of whether car is in gear or neutral. Can you suggest anything? Regards, XXXXX XXXXX


 


I have also just noticed that it does not start immediately.  It seems to happen once the car has been running for a time.

Submitted: 3 years ago.
Category: BMW
Expert:  Mike replied 3 years ago.
Hello and Welcome -

My name is XXXXX XXXXX Im sorry to see you have had a wait on your question.

Issues such as this can to be honest, be difficult to determine without physical checking of the car- From what you describe, its certainly not a known or common issue.

If it were a clicking sound then I would say its an electrical relay working overtime -due to the revs having dropped low - and you can get this due to low charge going then through the circuits...

If its more of a mechanical knowing - then it can be clutch related if a manual transmission or, and I would suspect more so, a fault with what is called the DMF - thats the Dual mass flywheel - these do have these faults as fitted. If that is suspect, you will never actually "see" any fault as its knocking inside the transmission bell housing - you would be best to have the car to the garage - have them with a mechs stethoscope - and they will trace the noise for sure that way then.

I do suspect the latter from what you have said to to be honest - and too - whatever the cause, that would be the best way to find / trace it down and get this cured for you.

Best Rgds, MIKE.

Let me know if you need anything more on this at all -

Please do click on the OK rating to Excellent ratings service for me now, Thank you for that... and you can get back to me anytime if you need / wish..

Best Rgds, MIKE.


Please note, you are rating the content of my "answer" - my help to you - not the "system" which can experience delays etc which are not under my personal control -or delays caused by "time -off" which we all have on occasion - Thank you.



Customer: replied 3 years ago.

Mike,

 

Very many thanks for this. I subsequently added a note saying the noise did not start immediately but once the engine had been running for a time and has had time to heat up. Do you think this is relevent and based on this is there anything you would add to your answer.

 

Also when you say 'mechanical knowing', did you mean mechanical knocking?

 

On the face of it I would describe it more as a clicking sound, although my wife reckons it sounds more like knocking. If what you say is the case regarding electrical circuits working overtime how can I rectify this. Thanks again.

 

Regards, XXXXX XXXXX

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