4.2 TDI engine noise
 

So, recent week my car has grown some kind of RPM-related engine noise. 2005 A8 D3 4.2 TDI (BVN)

It's not related to transmission or speed, present when in N/P just revving the engine. Cool/warm motor doesn't matter. Same goes for any load, present all the time but most apparent around 1000-1800 RPM, above that the engine itself drowns the noise.

Haven't been able to really locate the source but a qualified guess is anything going on the belt such as water pumps, AC compressor, etc.

Tried to turn off the ACC with the On/off button on the dash but not sure if there is any AC compressor clutch on this car. Turning off the ACC doesn't change the sound. Should turning off the ACC disengage the compressor?

Anyway, what is the best way to troubleshoot this? Hanging off the belt and see if goes silent?

Here's a video where the noise is present. You can hear a high-but-not-very-high pitched noise, a little bit like a sewing machine or something that follows the engine RPM.

https://youtu.be/sEZqyww4H8Y

Any ideas would be appreciated :)

Top two options would be PCV valve and low power steering fluid. Difficult to say as the video is recorded inside the car, so could potentially be other possibilities.

BTW Welcome to the forum. Pop along to the Introductions section and introduce yourself... and your car. We're a friendly bunch and appreciate seeing photos, lots of photos.

Thanks for the friendly welcome and two ideas to check out!

Guess I'll start out trying to listen to that PCV valve even though I have my doubts about that being the source. Location of that valve is pretty hard on the V8 diesel...

That sounds like bearing noise on an anciliary component. Try and record it from outside the car - both at the front of the engine and from the back of the engine near the firewall.

The D3 has an internally valved compressor I believe, so no clutch to turn off.

Will see what I can get. Moved from my house so now I don't even have a garage. Weather has been ****ty so it has to wait for the weekend. Meh...

Had some time today to listen to the engine while a friend was managing the throttle. Hard to locate any source or direction but probably from the back side of the engine, maybe little on the passenger side (hard to tell).

Engine otherwise runs like a charm, VCDS doesn't give any clues. I had an error on one of the EGR valves a month ago (before the noise appeared) but when I pulled them and cycled them with VCDS they worked just fine. No engine light since then.

I haven't followed up on steamships ideas. Just noticed that it was a pita to check the power steering fluid level. Noise doesn't change when I move the steering wheel though.

PCV valve? Hmm, hard to say anything about that. How would one know if that is bad? Would the sound come from it or would it just result in noise coming from somewhere else?

A shaky movie, held it in my hand while I listen around myself.

https://youtu.be/SsIXgsrMCVY

Sorry I can't offer any help/suggestions.
Good luck with it though and be sure to report back on any progress.

That definitely sounds like a bearings on something rotating. Could be anything from belt relay rollers or alternator/ AC compressor / power steering pump etc .

On another note my 4.2TDI also has a variety of noises the loudest /most annoying seems like a whistling kind of sound coming from the rear centre vents. It is rpm related but not directly, more like on a delay. For example no noise in idle but as you raise rpm the noise comes on slowly and if you stop at traffic lights or roundabout and rpm drop to idle the noise still keeps coming for couple of seconds and slowly dissipates, switching AC off does not affect noise at all. I notice that AC compressor shaft is a bit wet with oil and UV dye.

Check out the following two videos that might help. The first is a method of checking the various pulleys and tensioners to see if the noise is coming from them. Needless to say, once you've watched the video, if you attempt it, please be very careful.

https://www.youtube.com/watch?v=QyZWhz7uvDE

The second video I came across sounds similar to yours and may be worth checking out, although the location of the alternator may make it difficult to do what's shown in the video:

https://www.youtube.com/watch?v=hmPUUVwIJUU

Thanks for your time replying ;)

Some generic tips that seems like the next thing to do. Even though it is hard to say, it seems like the usual suspects around the belt (alternator, pumps) are not the guilty ones this time. I'll try to do some more directed listening but I prefer using a wooden stick instead of a big beefy screwdriver...

Also booked a time with my old trusty mechanics a few weeks form now. Just in case.