Knocking sound when engine is cold

[vstolpner]

I noticed a few times over the last six months or so that I get this knocking sound, and I thought it might have been my imagination, but recently it started to get more frequent. Wondering if anyone has experienced it or any ideas on what it might be?

It sounds like it's coming from the driver's side footwell, possibly behind the firewall. It only occurs at low speeds with low engine revs and when the car has been sitting for a while. At first it was only when very lightly accelerating in a corner, but now I noticed it when I lifted off the throttle in a parkade. Steering wheel position didn't seem to make a difference, but moving the steering wheel does seem to stop the knocking. Also it would only knock for a second or two and then not come back for a while.

Any thoughts more than welcome. I'm planning to take it to the dealer in the next few weeks as my warranty is running out (I do have CPO tough), but wanted to be a little prepared before coming in.

[kiloTHREE]

My first guess would be CV. Check your boots to see if any of them are torn.

[DUI Elite]

Originally Posted by kiloTHREE

My first guess would be CV. Check your boots to see if any of them are torn.

Same guess for me.

[vstolpner]

I'll have to check that out later today - thanks.

What would be causing the sound if that's the issue? And would it be normal for sound to disappear?

[kiloTHREE]

Originally Posted by vstolpner

I'll have to check that out later today - thanks.

What would be causing the sound if that's the issue? And would it be normal for sound to disappear?

If/when a CV fails, usually the boot gets torn from time/age or damage; dirt works it's way into the balls/cup of the joint and slowly starts grinding away at the surfaces. This drops the tolerances and creates play in the shaft. The clunking that you may be hearing is the engine and wheel taking up the slack whether accelerating or decelerating.

It may be something completely different like a loose tie rod/suspension/bushing/swaybar.

We can only guess.

[vstolpner]

Thanks. I'll check for loose components as well.

[Gamb1t]

Have you rolled down your window to hear it?
Is it on a certain steering direction?

Had a similar problem with my old mazda6 gt wagon. It turned out to be the ball joint. FYI make sure if they do replace any of the suspension bits, they would perform a wheel alignment. Are you still under warranty?

[vstolpner]

So had a quick look under the car over lunch - no visible damage to the CV boot, mind you there is a fair bit of rust on the differential.

Didn't get a good angle to give a good tug at the steering components so I'll have to do that later. Will check the ball joint then as well.

The car is still under factory warranty for another couple weeks. And then CPO kicks in, but I have no idea what would be covered there. Going to check with the SA when I'm there.