How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Mike Your Own Question

Mike
Mike, BMW Technician
Category: BMW
Satisfied Customers: 39198
Experience:  Tech Expert
9261905
Type Your BMW Question Here...
Mike is online now

Hi I have an m3 which is 4 years old, on acceleration there

Resolved Question:

Hi I have an m3 which is 4 years old, on acceleration there is a rattling noise coming from underneath the car - a similar sound to some small stones rattling in a tin can - what could this be?
Submitted: 2 years ago.
Category: BMW
Expert:  Mike replied 2 years ago.
Hello and Welcome...

My name is ***** ***** Im happy to help / advise...

With this situation, you could have small stones trapped under the car - or, loose exhaust shields - these things do need to be checked... Even at that age , you can exhaust shields / heat shields coming loose and causing this... and of course any car can get such trapped stones / debris under there too - so , a physical inspection needs to be done for these things...

Too - when under there - a physical check of the exhaust / catalytic converter and silencers needs to be done... they can fail internally so that the plates / baffles come loose and rattle inside - if the exhaust is literally thumped hard along its length - if it rattles as you describe, you have found the fault - and that section would need to be replaced.

If nothing is found, then your symptoms do as well sound to be a condition called "pinking" that can occur when the knock sensor ( or other )is failing.... for this to be found / diagnosed properly and fixed, it needs to be checked with plug in diagnostic equipment. Basically when the knock sensor / circuit is faulty, ( or other engine management fault ) you get what is called "pinking" - which is pre detonation in the cylinders - which then produces "rattling" - like as you describe - stones rattling in a tin.

Im very pleased to have helped you - Do let me know if you need anything more --

*** Meanwhile - - >>>> Please do click on the "OK/ Excellent ratings" for me - Thank you in advance for that...

You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..

Kind Rgds, MIKE.
Mike, BMW Technician
Category: BMW
Satisfied Customers: 39198
Experience: Tech Expert
Mike and other BMW Specialists are ready to help you

What Customers are Saying:

 
 
 
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil
< Previous | Next >
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil
  • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles
  • As a single woman, I really appreciate an excellent and affordable opinion.
    Thank you Geordie, I will not hesitate to contact justanswer in the future!
    Sue
  • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff. Jim
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C.
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex
 
 
 

Meet The Experts:

 
 
 
  • Matt

    Matt

    Mechanical Engineer

    Satisfied Customers:

    98
    BEng hons Mech engineering, in auto industry 22 years
< Previous | Next >
  • http://ww2.justanswer.com/uploads/35/350matt/2012-6-7_182356_matsavatr.64x64.jpg Matt's Avatar

    Matt

    Mechanical Engineer

    Satisfied Customers:

    98
    BEng hons Mech engineering, in auto industry 22 years
  • http://ww2.justanswer.com/uploads/Guest/2008-02-15_191551_avatar.jpg Roger's Avatar

    Roger

    BMW Master Tech

    Satisfied Customers:

    2823
    10 yrs. experience as BMW Master Technician, shop foreman and dealer.
  • http://ww2.justanswer.com/uploads/FO/fordtwo/2014-12-19_163422_arrepair.64x64.jpg Robert's Avatar

    Robert

    BMW Technician

    Satisfied Customers:

    83
    Fully qualified 19+yrs exp/self employed technician in the UK
  • http://ww2.justanswer.com/uploads/IN/indytech/2013-8-8_102717_SantoDomingo146598x6402.64x64.jpg Greg's Avatar

    Greg

    Technician

    Satisfied Customers:

    1095
    Automotive diagnostic tech
  • http://ww2.justanswer.com/uploads/TE/techmachine/0601821347169_717372168_8940977_39623330_o.64x64.jpg Ross's Avatar

    Ross

    Diagnostic and repair technician

    Satisfied Customers:

    467
    Licensed diagnostic and repair technician
  • http://ww2.justanswer.com/uploads/RO/RobMechanic/068.64x64.JPG Rob's Avatar

    Rob

    ASE Certified Technician

    Satisfied Customers:

    82
    30 years trade experience