Hi all, I have had multiple Disco's over the years but my latest issue has me scratching my head. I have a 2004 Discovery II w/ 92k on it. I have had it since 2007. As of late there is a strange knocking sound heard inside the vehicle after it's warmed up. I would call it a "rhythmic knock" that starts fairly slow then begins to speed up to a point where it just spins up and disappears.

I captured it on video. Note: The knocking gets even faster than what is heard in the video:

https://drive.google.com/file/d/1tJI...ew?usp=sharing

I only hear it inside the vehicle from what seems like the drivers side. The engine is surprisingly quiet for a 4.6. No knocks or clicking heard from motor and it seems to run great. I have a close relationship with some techs at my local dealer. Some of them mentioned it could be a tapping from an emissions device or maybe something tapping on the firewall? I would assume if this is the case I might hear it from the engine compartment?

Any thoughts? It's driving me insane..

 

Does this happen when you are driving or at idle? If when driving and it goes away, it might be something banging against muffler, drive shaft etc.

 

I should have mentioned previously but it seems to be most audible when the vehicle is at idle. I can also hear it faintly underway but I think the drivetrain noise drowns it out. Once the vehicle is warm it will begin.

​​​​​​Starts slow and steady then will speed up to the point where it sounds like a clock at 100x speed. Then just goes away only to return again maybe 30 seconds to a minute later.

 

That’s an odd sound. Can you “feel” it as well as hear it? I assume RPM doesn’t change the rate or loudness of the sound? It could be something electric like a stepper valve or something malfunctioning. Do you have SAI? Have you checked the IAC? I would put your hand on components when you hear the sound to see if you can track it down.

 

Okay, so if I understand you, you only hear this in the cabin. At no time have you heard this when you are sitting in your driveway and the car gets up to normal temps and you are standing near the engine? I am asking because it sounds like the beginning of a slipped sleeve or a collapsed lifter. I know my ticking sounds started at about 100K. I bought my '04 in 2011 with 55k. At 174k, my head gasket finally went. In the tear down I discovered 1 collapsed lifter and a sleeve that slipped.

 

Thank you all for the help!

So the noise is only heard in the cabin. At no point do I hear it anywhere in the engine compartment. The engine is actually nice and quiet for a 4.6. I have listened for prolonged periods in and around the engine and do not hear this knock or any ticking for that matter.

I have thought about the potential for a slipped liner but I would think I could hear that from the motor itself or the lower end and not the inside of the vehicle.

Also what's odd is the speed & frequency of the knocking sound. It will start slow and rhythmic but will then speed up to what sounds similar to an old bike with a card in the spokes so fast in fact that it becomes imperceptible and returns later at the slower speed and the cycle begins again.

The speed of the sound does not match RPM's and I can faintly hear it doing it's thing underway but the drivetrain & tire noise makes it difficult to hear. Its most perceptible when the vehicle is warm and sitting at idle. It will then come and go indefinitely. Seemingly from right behind the drivers dash or center firewall area.

Any idea on where I can find the IAC ? I will try to see if I can't feel the knock from the component when the sound is occurring.

Note: the vehicle is equipped with SAI.

 

Is it possibly pieces of your catalytic converters swirling around in the housing?

 

One would think but my cats were recently stolen from the vehicle and are brand new.

The noise occurred prior and continues after cat replacement.

 

IAC= Idle Air Control Valve? They are very quiet never heard one that was loud or could be hear in passenger compartment.

For what it is worth, I could never localize the sounds of my collapsed lifter or my slipped liner. Only when the engine was taken apart did I find them. Also, a great many people here have rune for many miles without dealing with it. I ran for at least 60,000. You may wish to try a product that combines with oil to flush out engine. Do it several times. What oil do you use?

 

I run Rotella T5 10w-30 Synthetic blend w/ wix filters.