Any Thoughts On Where Noise Is Coming From
 

I've had an unusual whining noise from my car, but only under normal acceleration. Depending on the road noise, it can be heard from speeds of 30 to 70mph (it sounds like it's coming from the transmission tunnel which is why I put it here). It's been there ever since I bought the car four years ago and finally decided to try and capture the sound.

I've uploaded a video clip to YouTube, if you want to listen to it. The link is as follows:

https://youtu.be/f1dh6RcGf5Y

You can hear it best around the 20-30 second mark, and see when I'm accelerating.

I don't know if this has anything to do with it, but I just discovered that one of my intake manifold actuators isn't working properly. Looking from the front of the car, it's the one on the left. I just happened to see another video on YouTube of how these work, and since I was using my GoPro today, I thought I'd capture these as well. They both deflate when the ignition is turned on, but only the right one inflates when you rev the engine. Both inflate again when engine stopped.

I would be pretty sure that the noise is not related to the manifold actuation. It doesnt sound too good though, I am afraid to say. Did you not get the tx serviced at one stage at Mackies? If it has been there since you've had the car then it (surely?) would have been picked up there? But it certainly sounds drive train related.

It sounds to me something more like a washer or shield or metal fixing rattling, maybe just something on the undertray?
If it was inside the transmission, with all the lubricants/fluids, that type of noise seems implausible.

Have you checked for loose heat shields. I had one once (on a Beemer) that was bolted up tight, but the shield had broken right around the bolt head. Result, it looked OK, but at speed would free up and make a racket

+1 my thinking also

Could it be related to the air conditioning? I know mine makes a little noise, not like that though. :Confused:

Yep, got it serviced with them in October 2014. They did say there was signs of wear, but didn't elaborate. At that time, there would have been about 67,500 mile on the clock.

HPsauce/tonupkid - Just wondering if you're listening to the wrong noise. There is a noise at the very start and around the 10 second mark (like crackling from a LP). Ignore that, as that was from the GoPro resting on my left foot. I get what you mean by something loose causing it, but it doesn't alter with speed (which I would have expected). The only change in tone is when you take your foot off the accelerator and the noise stops. I was doing about 30mph when I did that video, but it would sound the exact same at 60mph.

Wasn't sure if the GoPro would pick up the sound at all, so closed the windows and sunroof, and turned off all the A/C and fans.

I've done the usual Google search of whining related noises from engines and transmission (both Audi and generally), but nothing I find seems to relate to my problem.

It could be a bit of noise from the exhaust? I had a similar noise under load when I first rebuilt the engine. Turned out it was the manifold-exhaust pipe joint on the driver side joint 'bedding in'.
It was such an awkward pig to get at I finally got a couple of turns at the nuts after 3-4 months and it seemed to cure the problem

Given that its throttle-related and not speed-related I would say it's forward of the flywheel and not something rotating. The way it behaves with the accelerator pedal says vacuum / intake leak to me.

The manifold pods might actually be a clue - if one of them has a split diaphragm it could be making a noise as its leaking. Possibly it could be a leak in part of the SAI valve system which reduces the vacuum such that only one pod can activate. Possibly something around the throttle body boot / oil separator.

I would first try disconnecting the vac pod solenoid valve, just to rule those out. It will throw a code but thats easily cleared. If that doesn't affect it, have a good look around the back of the engine with a torch looking for split hoses.

Pretty sure I got the right one, when you put your foot down it's there. Suggested to me that very slight movement of engine/drive/whatever under load was releasing something metallic and dry. Constant noise as you said so not rotating, hence my suggestion.

And aren't manifold flaps mainly rev-related, though obviously the vacuum driving it is somewhat throttle-related. You could check that by manually overriding gears.

Cheers all. I shall investigate all suggestions and see if I can uncover anything.

Just an update on this. Disconnected both vacuum pod solenoid valves and took it for a short run as well as doing a few errands, but noise was still apparent. I also checked both diaphragms on them and no apparent splits or holes.

I had a look at the pipe coming from the SAI pump and that is fine. I'll check all the vacuum pipes tomorrow when the engine is cold, although I had replaced the majority of these a couple of years ago.

There are two of the vacuum pipes that I'm not sure where they go. Each goes from the front of the engine to either wing, seems to connect to a stiffer plastic pipe and then disappears up towards the bulkhead. Any idea where these head off to?

I'll also get it up on ramps and check that heat shields and anything else lurking around is firmly secured.

They go to vacuum reservoirs in both front wings. If you disconnect the hose at the junction after the engine has been running there should be a brief hiss as the vacuum is released.

Cheers MJ. Just got my version of ETKA up to date and checked it out. I might do what you suggest, as that will test their integrity, as well as me checking the rest of the vacuum lines.

Well, today I replaced every single piece of vacuum pipe under the bonnet. Did it one piece at a time in case I forgot where the bits went. There was only one piece that was showing its age, and that is the one at the front that goes to to top of the engine on the left side, down the side and then across to the plastic pipe leading to the vacuum reservoir in the wing. Difficult to say if it had any leaks.

Started it up and left it idle for about 10 minutes before taking for a short drive, but the noise is still there. I did check that everything was secured including the heat shields down the sides, but I forgot to check the ones underneath this evening whilst doing another little job.

I also did another little video to check the vacuum pods and noticed that one of them seems a bit hesitant to move. I doubt it has anything to do with the noise I hear, but it looks like I may be attempting this job at some stage:

40V Intake manifold fix for stuck or sluggish flap pivots

Just a random thought, could the gas pedal actuator itself be making the noise? its a little barrel shaped object connected to the gas pedal. Does the noise seem to be coming from inside the cabin?

I think I see what you're getting at. If you mean do I get the noise only when I press the accelerator and the noise then stops, then no. As long as there is a load on the engine, then the noise is there. The video may be a bit misleading as I was trying to show when I get the noise, but as it was short bursts, it could look like that.

Think of if you're driving along the motorway at 70mph. You will hear the noise constantly. You then notice up ahead that traffic is getting busier so you ease off the pedal to slow a little. Just doing that is enough to stop the noise, until you put your foot on the pedal again.

As to where the noise is coming from, I'm tempted to say that it comes from the transmission tunnel, but as we all know by now, cars seem to move sound around so it sounds like it's coming from somewhere else.

I had thought about putting the GoPro on the outside, but then you pick up wind noise or tyre noise. I'm not even sure if it can be heard outside.

I was thinking of the accelerator electronic mechanism, as long as its not at rest it could make a noise? I dont know exactly how it works but it can move the gas pedal on its own when in cruise control, check it out its freaky :). When you press the gas its constantly under some sort of tension. I assume it must be electrical since it has no vacuum hoses going to it possibly its some sort of solenoid to move the pedal electromagnetically?
However that should mean it would make a noise even when car is stopped in neutral and revved.
Maybe there is nothing in there to make a noise anyway.

http://forum.a8parts.co.uk/attachmen...1&d=1495610347

The pedal only moves (very slightly IIRC) with the PF cruise control, Sean has an FL model where it's all integrated into the engine management, no separate module.

Ah, ok, maybe I got confused with my old car, a Volvo, that pedal definitely moved when pressing the + / - button on the cruise control. Its a long time since I used cruise control on a D2, it doesn't work on my current car it only worked on my previous S8 and that was 4 years ago.

It didn't register with me last night that you meant the TPS, until I saw the picture.

I did replace the TPS in the last year or so due to the erratic throttle response I was having, that Andrew was also experiencing, and since I've had the noise all along, that also rules that out.

But at least this has eliminated something else as the cause.

If you rev the engine in neutral, with car stopped, does it produce the noise? Just in case it is linked to throttle + speed

Have only been out in the car a couple of times, but did remember to try this both before and after a journey, and it doesn't produce the sound.

I checked every heat shield and they all seem secure enough, and also made sure everything else was secure.

I also have another suggestion worth considering. When I was out on Friday, I had the windows down to get some cool air in, and happened to drive along a stretch of road with a long wall next to it. To my surprise, I heard the odd noise being reflected off the wall (confirmed by easing off the pedal). Later on I was looking through ETKA for something, and came across an image which shows a bearing supporting the rear prop shaft. If this were worn, is it possible that this could be causing the noise?

Only thing is, I don't recall seeing anything like it when I was last under the car.

Hmm that is a viable culprit, and would normally be load related as the prop does move about a bit between acceleration and overrun. I've no experience of how Quattro behaves when that bearing is worn, but I do have an A4 prop in the workshop with a very loose rattly bearing so its definitely possible for them to fail like that.

IIRC you can't actually see the bearing on the D2 as it's hidden by the heat shields. To get to it you would need to remove the exhaust system and obviously the heat shields and then you can inspect and / or drop the prop. If the bearing is worn enough to be noisy its likely you'll be able to feel some play in it.

Typically Audi, you can't actually buy the bearing separately as the prop is balanced as an assembly and the bearing is non-trivial to change. People have found solutions for the smaller models, but I'm not sure about the D2. Its easier to just change the whole prop for a good used one.

That would explain why I didn't see it. Doesn't sound like an easy job just checking it, especially without access to a lift, so will have to think about it.