Engine making ticking/knocking noise when idling

438593839

MEMBER
2013 AUDI A8
4.0L
V8
TURBO
4WD
AUTOMATIC
125,000 MILES

Hello,

The vehicle listed above is an A8L 4.0T. Engine recently started to have a ticking/knocking noise. It can be heard from the outside of the car, especially with the hood open. It cannot be heard from the inside with all doors and windows closed. It sounds like it is coming from the driver's side of the engine. The car runs perfectly fine and shows no fault codes. I attached some videos showing what the noise sounds like. Hope some experts can help me identify the cause of the problem.
Thanks in advance.

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7 Replies

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Hi,

Does it seem to be louder under the vehicle or at the top? Listening to the video it seems to be louder at the top, but I'm not there to be certain.

If it's louder at the top, it sounds like it could be a lifter failing.

Take a look through this link and let me know if it helps. Also, let me know about the location of the sound (top or bottom).

https://www.2carpros.com/articles/engine-noises

Take care,

Joe

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Sunday, June 19th, 2022 AT 10:43 PM

438593839

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9 POSTS

Hi Joe,

Thank you for the info. I can’t really tell if the noise is louder at the top or under the car. It sounds about the same. Also I captured another noise today (see attached video). It happens randomly at idle and if I give it a little gas it will disappear. Also the oil filler cap seems to have some suction force as you can see in the video. Could that be related? Any thoughts on what the problem might be?

Thank you for your help.

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Monday, June 20th, 2022 AT 8:53 AM

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Hi,

I listened to the video. I'm really not hearing a ticking from the engine in this one. I did in the original videos. Am I missing it?

As far as the vacuum is concerned, when removing the oil fill cap, that's normal. There is a vacuum in the crankcase provided by the PCV system to draw out unburned gases in the combustion chamber. It draws it back through the intake to be returned again.

I just relistened to the first videos. It could be a lifter issue, or it could be something from one of the belt-driven accessories. Are you comfortable removing the serpentine belt to check each of the accessories for play? Also, you could spin each one to see if you could recreate the noise.

Let me know if I am missing the sound in the video.

Take care,

Joe

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Monday, June 20th, 2022 AT 10:17 PM

438593839

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9 POSTS

Hi Joe,

I took another video. The ticking noise sounds clearer from the driver side/bottom of the car. The only belt driven accessory is the generator which seems to be working fine.

Also, I have to mention that I modified this car by replacing the hydraulic steering with an electromechanical steering (all OEM parts of course). All parts in the hydraulic system (hydraulic rack, fluid, hoses, etc, ) have been removed, except the hydraulic steering pump. It is attached to the lower rear driver side of the engine and is chain-driven (as you can see in the attached pictures). Right now, the pump is just running empty and useless. So, do you think the noise could possibly come from the hydraulic pump?

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Wednesday, June 22nd, 2022 AT 11:00 AM

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Hi,

If the pump is empty, that is certainly a possibility. The bearing is lubricated by the power steering fluid. If there aren't any, it will make noise.

Are you able to disconnect the pump from the drive belt? That is what I would do to determine if that is the issue. I suspect it is.

Are they still using a coolant-cooled alternator? LOL I used to work on these often. Well, I did a lot of yelling because there was never enough room to work on them. My favorite line from the manual was, "Step 1, remove the engine". LOL

Let me know if you can remove the serpentine belt to see if the sound is gone. Do not run it that way. Only for a few seconds to determine if the sound is gone.

Let me know.

Joe