Clicking clunking noise with brake pedal pressed and in reve

[StillLearning]

I have a 2011 Nissan Micra, manual 1.2 petrol. Its making a clicking/clunking noise but only in a really specific situation. 

With the engine is running and the car is stationary - when I press the brake pedal and also put it into reverse keeping the clutch depressed. The noise stops when I release the brake pedal, or when I lift the clutch or move the lever into a different gear.

I've attached a video to explain it better - its the repeated, rapid noise about 6 seconds into the video.

Would anyone have any ideas of what the problem might be, or anything I should be looking at?

https://imgur.com/a/bg1VKmj

Edited by StillLearning on Thursday 25th May 11:37

[GreenV8S]

I don't get any sound on that video. I can't see any internal mechanisms that would be common to all those factors. Does it sound as if it could be a clutch cable, part of the gear linkage or similar fouling a moving part of the engine?

[StillLearning]

I've updated the link, so hopefully it's make some noise now.

It's a regular, metallic sounding clunk.

[CrutyRammers]

That's well weird.
Sounds slower than the engine speed. Does it increase if you rev the engine? (get another foot!)
Sounds almost like a pressure being released, like a "cough" or something.

[CrutyRammers]

If it's slower than the engine speed, it'd have to be downstream of the gearbox; but if the clutch is depressed then that shouldn't be turning. There'll be various pumps turning at different speeds but the brake pedal wouldn't have anything to do with that, neither would the clutch; unless it's something really odd like crankshaft endfloat and the clutch release pushing it ?

[StillLearning]

It doesn't increase speed when I increase the revs - just tested with an umbrella for my spare foot!!

[StillLearning]

The bit that seems most confusing is that the noise only happens with the lever in reverse, not any other gear - the clutch is depressed so surely it shouldn't make a difference which gear is selected??

[CrutyRammers]

So it's nothing getting caught by the engine spinning round then, which is good at least.
Do modern brake servos have any pressure management in them or something like that I wonder, so holding the brake pedal down is causing a valve to keep opening/shutting?

Sorry that's a bit of a mystery.

[GreenV8S]

Is it the knock happening every second or so?

[StillLearning]

Yes, that sounds about right.

[tux850]

I couldn't hear the sound at first - just your neighbour whacking in fence posts with his hammer... but then the penny dropped!

It sounds quite like a sound of some significance - is it as prominent as the camera mic pickup makes it sound? If you can get someone else to do the pedal work might you be able to narrow it down the source in the engine bay?

[tux850]

Random thought that will likely lead nowhere...

The path of logic would suggest that with the clutch down the gearbox is taken completely out of the equation (if we assume no binding of the friction plate etc) and so what else happens when in reverse gear given that this action does seem to be significant? Well one thing is that your reverse light illuminates... And similarly of course your brake lights will be on too... Could there be some explanation as to why you'd get a noise when both sets of lights are on? Quite what I don't know.... Electrical loading, dodgy earthing or something I'm not quite sure.

Almost certainly a red herring but I'd be tempted to either disconnect the reverse sensor (or removing the bulb might be just as good) just to rule it out and move on!! Maybe even do the same with the brake sensor/bulbs whilst you're at it for completeness.

Edit: Ah... Lifting the clutch stops the noise doesn't it, yet the lights would all remain on... It might still be electrical/lights-related though, just not exactly sure in what way.

Edited by tux850 on Friday 26th May 10:18

[GreenV8S]

StillLearning said:

Yes, that sounds about right.

If it's that obvious, you can probably locate it by having somebody else in the driver's seat and just track it down by ear. Be careful to stay away from moving parts under the bonnet.

Given the low frequency, I suspect you're looking for something hitting resonance or a system cycling through different states (aircon pump, brake booster, that sort of thing).