My mazda 3, AT makes a slight knocking sound when I suddenly press the accelerator pedal, and the engine is at low RPM and the gear is high.

e.g. 1500rpm, 4th gear, at 40 km/h

ATF Oil was changed already a few months ago.

Where could the sound be coming from?

  • Do you get the knock if you shift from drive to reverse and then drive again? – mikes Mar 18 '15 at 9:31
  • Where exactly does the sound emanate from? Does it sound like an engine noise or does it reverberate through the cab as though the noise is coming from the body of the car? Also, if you have your gear selector in 4th gear, with an AT it doesn't mean the tranny is in 4th gear. I take it if you step on the gas it is not down shifting? – Pᴀᴜʟsᴛᴇʀ2 Mar 18 '15 at 10:23
  • Mikes: sometimes it knocks when I engage the reverse when I'm parking. The shift stick vibrates. – Andrew Tan Mar 18 '15 at 13:05
  • Paulster: it seems to come from the transmission. I can feel like something blocking or stopping the turning motion of the wheels. Transmission is in manual mode (steptronic) – Andrew Tan Mar 18 '15 at 13:05
  • In the future, please put an "at symbol" (@) in front of the person's name (ie: @mikes ) so we'll get notification :D It's all a learning curve! – Pᴀᴜʟsᴛᴇʀ2 Mar 18 '15 at 13:21

My mechanic checked today. It was the lock bolt that was loose. he tightened it and the knocking sound went away.


That's item no 2 in the link above.

I shudder to think what would have happened if it came loose. Wouldn't that make the car spin?

  • I can't see it in the picture but typically there is a locking pin that goes through that bolt. – stoj Mar 21 '15 at 16:47
  • Considering the components which have to be removed to get a CV axle out, there would be a considerable amount of noise before anything catastrophic happened. Long term it could accelerate the failure of the CV joint and if that joint failed then you would have a steel bar whipping around under your car. – Lathejockey81 Mar 21 '15 at 17:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.