Noises VP37: Source of Rattling Sounds

Hello everyone,

A solution (for a trivial problem) and a question...

Last weekend, I took out my air filter because I read in the service booklet that it hadn't been changed at 15,000 km. I then thoroughly vacuumed it, as Bertil mentioned a while ago, and cleaned the air filter housing from a pile of leaves .

While it doesn't necessarily improve handling, I have the impression that it consumes about 0.2 to 0.4 liters per 100 km less when cruising in the city (1100...1200 RPM) at the same driving style – which is something, especially considering that it also protects the turbo.

During the test run, I noticed a loud knocking sound that was probably being masked by the engine insulation. The cause was simple and easy to fix, so I'm just mentioning it here in case anyone else experiences similar issues.

The sound dampening cover on the engine (the part where "TDI" is written) is fastened with three studs, and is dampened by rubber elements pressed into the cover. These are shaped in such a way that they both keep the cover at a distance and act as a buffer between the nut and the cover itself. One of them was completely destroyed in my case (I suspect a mistake by the workshop during assembly), so that the upper part (between the nut and the cover) was almost completely crumbled. The stud is designed so that it becomes thicker at the bottom, which prevents the rubber from being crushed. In this case, it resulted in the cover having a vertical play of 0.5 cm - one can imagine how much this would rattle in a TDI at idle. A piece of silicone rubber was severely damaged.

And now, the question:

In this context, I started the car for the first time without the acoustic cover, and I noticed (normally you only hear this with my car if you're standing directly in front of it, which you don't do when starting it) that the ESP makes a rattling noise for about 2 seconds when the ignition is turned on (engine still off). I think this might be related to the pre-injection or the fuel quantity control. I tried this again after tinkering with it and driving about 30 km, with the ignition on and listening, and it was silent, whereas before, with the same ignition sequence, it was clearly audible (and this happened multiple times, on and off).

Does anyone have an explanation? What is considered normal behavior in that situation? What is different (besides the heat) after a drive compared to after two hours of idling and one minute of running in neutral?

Best regards,

Jan.

Deleted upon request.

Hi Gustav,

Thank you for your comprehensive answer!

Your version 1 seems more reasonable considering the explanations, but I'll continue to observe it. (Does it only work with two people? Because with the hood closed and the cover on, you can't hear it in the driver's seat even with the door open, but you can hear it in front of the car.) During a cold start, it should be audible more often or always.

Zum Geraeusch selbst noch: Meine Eltern haben einen grossen Gas-Heizkessel, der elektrisch gezuendet wird. Das geschieht ueber Zuendimpulse, die einen kleinen Moment vor der Aktivierung der Gaszufuhr eingeschaltet werden, und dann abschalten, wenn die Flamme gezuendet hat. Das gibt so ein ratterndes Geraeusch (eben die ueberschlagenden Funken der Hochspannungszuendung), und dieses Geraeusch ist fast genau das gleiche, das die ESP an der Stelle gemacht hat. 50...60 Hz sind das eher nicht, auch das spraeche dann gegen die 2. Variant.

Best regards,

Jan.

I also hear this ignition pulse sound during normal idling, even without the cover.

AFN 212,000 km, chip.

What is that?

Regards,

Manuel.

Deleted upon request.

'The strange thing about my engine is that it's so quiet since the chip tuning that you have to listen very carefully with the hood closed to tell if it's a diesel!'

Okay, the A4 is already remarkably well soundproofed!

Regards,

Manuel.

Hi everyone, especially Gustav,

I conducted some new experiments today:

The car was cold (it had been sitting for 20 hours). I turned the ignition on, and there was a rattling sound that lasted about 2-3 seconds (exactly the noise described). If you're quiet, with the radio off, no traffic noise, and the driver's door open, you can actually hear it from there as well.

I drove 3 km to a gas station, but I didn't hear that noise there (although it could have been due to the noise from other people trying to get to the pumps). I didn't try any further tests.

37 km (city highway, fuel consumption: 4.1 l / 100 km) later, arrived at the destination. Ignition off, then on again, no sound, and this persists even after repeated attempts.

5 hours later (so not completely cold), I turned it on, and I heard a noise. When I turn it off and on again, the noise reappears, and this can be repeated multiple times.

After another 37 kilometers, it was impossible to provoke it.

Based on the experiences from last weekend and this one, it seems that the issue doesn't occur when the engine is at least somewhat warm (I'll test that with the 3 km driving distance again). However, just idling for a short time isn't enough to prevent it.

As far as I'm concerned, this still fits very well with the possible cause mentioned by Gustav under (1) - what do you think?

So, the noise would therefore be harmless?

Could someone else with an ASV (presumably the ALH is similar) test this as well?

@Gustav: By the way, like the entire car, the ESP now has 25,500 km on the odometer, and it has only ever run on diesel.

Best regards,

Jan.

Deleted upon request.

Hi Gustav,

You're right, I've corrected it in the post accordingly.

You wrote above "can occur" - was it possible to "only" observe the effect through measurement at the pump where you measured it, or did it also make exactly the same noise?

Otherwise, I'm also curious to know if there are others who experience similar noises, or if my ASV is an exception for some reason.

Best regards,

Jan.

Deleted upon request.

Hello,

Regarding pump noises, here's something from my experience.

A 1997 AFn makes a clicking sound when the ignition is turned on.
With the pump cover open, you can see how the valve quickly reaches its maximum position (with a click) and then returns to the zero position (with a click).
The noise disappears when the engine is warm. However, I haven't checked to what extent the valve gear is still being moved in that case; the pump is simply too hot for me to mess around with it.

The 2001 ALH (Ibiza) makes a whining noise for a few seconds when the ignition is turned on, but it doesn't click. It's probably the same issue that Jan observed.
Since that's my wife's car, I drive it less often, and I haven't consciously experimented with its behavior in relation to the engine temperature.

Hi Ulf,

It seems that the ALH is indeed behaving exactly like the ASV. Could you please test two things at your convenience?

1. Turn the ignition on, wait (you should hear a sound), but don't start the engine. Turn it off again, then turn it on again, and you should hear the sound again (this can be repeated as many times as needed).

2. Turn on the ignition (according to my attempt today, 2 km should be enough), and the noise shouldn't occur.

Best regards, and thank you.

Jan.

Jan6K wrote:

Could you please test two things at your convenience? 1. Turn the ignition on, wait (you should hear a sound), but it won't start. Turn it off, try again, you should hear the sound again (this can be repeated as many times as you like).

Yes, that's correct.

Quote:

2. Turn on the ignition (according to my attempt today, 2 km should be enough), as the noise shouldn't occur then.

It seems it will happen, but it will be significantly shorter (estimated at about 0.5 seconds, I had the hood open) and it will end with a click.
I can't be certain that it's the same sound as in example 1, but I'm 90% sure (I don't have "frequent" opportunities to test it on Ibiza).

Hi Ulf,

Thank you for your attempts!

That doesn't necessarily contradict my observations... I haven't personally heard the "warmest" sound yet (I always turn the key ), but there's definitely a clicking sound. I'll try listening again with the hood open, but I think it will probably end up being the same as what you experienced, Ulf.

Conclusion would be:

COLD: Test mobility by repeatedly moving it back and forth, which produces a squeaking sound and likely generates a small amount of heat.

CAUTION: Move it only once, then leave it alone, so it doesn't get any hotter and nothing happens to the spools.

Best regards,

Jan.

Hi everyone,

Here's another addition:

I repeated the entire process again, and I get the EXACT same result as Ulf. It seems like this is normal when generating ALH/ASV data.

Best regards,

Jan.