I've had this car from 100k to now which is at 180k, about ~10k-20k this has been happening, It's not from the octane/fuel I've changed all the spark plugs with nkg platinum, and filled it up with mobile 1 fully synthetic oil.

I hear the noise first right as I start the vehicle. When revs go back down to idle, right before it hits idle you hear a very faint knock and the stops at idle.

When I start going around a constant ~1,000-~2,000 rpms with a constant fuel pressure (that's when it can be hear the clearest) when I start up to ~2.5k rpms or higher the noise is gone.

And finally I can hear the noise right as I turn the car off. right as the car turns off from idle, you hear a faint knock before the engine turns off.

Any ideas?

Thanks in advanced, Andrew.

 

knocking or clacking? Does the noise rate of knocking increase and decrease with engine RPM, vehicle speed, or neither?

Would you think of it maybe as a sort of rattle instead of knock based on the pitch of the sound?

 

It's more of a rattling/clacking instead of a knock. This noise doesn't increase or decrease with engine RPM, and only hearable between low revs ~1,000 - ~2,000 anything lower or higher it doesn't sound.

I've tried looking for a loose screw/bolt that could be just hitting something, no luck, i've tired to locate a general area, havn't been able to get underneath the car to evaluate where it's coming from, but it does sound like it's from the back of the engine near the intake.

I did a few test to figure out if it's all gears if it sounds, i put it in R, held the brake reved it up to 1k-2k nothing.
Did that in D heard nothing (Pressing brake)
Did that in P heard the noise (Obv not pressing brake)
Did that in N heard the noise

I also went to the movies a few nights ago, and heard the rattling while coasting with a constant fuel pressure while in 1st gear.

The noise can be heard loudest when the car revs back down from a higher rev, IE: Rev to 3k heard at 1k-2k, is louder than just revving the car to 1k-2k.

 

timing chain

 

timing chain rattle would increase with RPM.

maybe fuel dampers? Search for fuel damper rattle on a Murano forum for a quick check

 

this could be a shot in the dark but maybe heat shield i just got mine tightened and when i first heard it because of the way sound traveled it sounded like the engine

 

That actually sounds promising, i'll check this tomorrow, tighten it down and have a friend rev the car a bit while i'm under the vehicle see if i can see exactly where it's coming from. another friend also suggested the heat shield.


Not sure how to check this, i googled search that but found nothing. Could you help me?
It said something along the lines of checking the pcv hose, and see if there's fuel in it, if there is then the damper is bad, there's no fuel in it. so if they are correct it isn't the damper, let me know if this is correct or not.
Thanks


Side note:

I ran sea foam through the fuel vacuum hose. to clean everything out, car was pretty clean but the noise is still there, same as before, not on idle, low revs 1k-2k loudest when engine revs drop down with NO throttle pressure. (so i am leaning more towards the heat shield)

I'll update more when i inspect tomorrow.

 

basically, if your car is an auto, put it in auto with the parking brake on or someone holding the brake down. If your car is a 6 speed just start it and leave the parking brake on. pop the hood and put a stethoscope on each fuel damper one at a time. The fuel dampers are on the end of the fuel rail, one per bank. If you hear a "clank clank clank" through the stethoscope then the damper is bad. If you dont hear anything its fine

 

Checked the Heat shield, isn't the heat shield but i did find that the rattle is louder from underneath, near the flex pipe and the oil pan. it's not the heat shield. i took one off, that was barley hooked on their. the front pipe / flex tube look pretty rusty.

What do you guys suggest, i don't see any leakage and i don't see any loose bolts. but it sounds like its coming from the pipe that goes up from the exhaust to the front of the engine, didn't take car on lift and can't really see what that pipe is or where it actually goes, but it definitely something to do with the exhaust.

I'll check the dampers when i get my hands on the stethoscope

Thanks.

 

Video of the nosie, hopefully this gives a better idea.

 

well at least youve got it narrowed down to the exhaust. uhm id say get it up on a lift and start tapping around. its probably something extremely simple but annoying as hell to find as are most frustrating sounds

 

Pre-cat rattle

/thread

 

yeah, definitely not dampers