Weak, intermittent grinding/rumbling noise from engine area

[SinWin]

Hi! 

I've got an Audi A3 from 2008, with the 1,6 liter petrol engine. Lately, I've noticed a weak rumbling or grinding noise from the engine, which follows the engine revs. The noise is not constant, rather like a ticking clock: "rumble, rumble, rumble". It sounds like some kind of vibration of metal or a belt running over something it shouldn't be running over — kind of hard to describe. 

The noise is accompanied by a weak humming noise in the cabin, but I'm not sure if this is from the engine compartment itself or just some plastic in the cabin vibrating. 

The noise isn't always there, but I've heard it when the engine is both hot and cold, and in hot, cold, dry and wet/humid conditions. 

The attached file is a recording I made yesterday of the noise. Please note that I've cranked the volume up to make it easier to note the sound: it is not very loud in real life, but is coming from the engine area somewhere. 

Does anyone have any suggestions as to the source of the noise, and how to fix whatever is the matter?

 

engine_noise_audi_a3.wav

[Trevor]

Hi...and welcome to the Forum

I'm sorry but I can't play the video, can you send it as a MP4 please?

Cheers   Trevor

[SinWin]

Hi, and thanks! 

I've attached the file again, this time as an mp3-file (it's audio only). 

I should mention that the sound is there both at idling, and driving, clutch engaged and disengaged. I'm not sure if it disappears when driving at higher speeds, or if it just drowns in general noise from the tires etc, but when driving at city speeds it is noticeable. Turning the A/C off does not make the sound disappear, nor does shutting down air circulation completely have any effect. 

Regards, 

Sindre

engine noise audi A3.mp3

[Trevor]

That is a most peculiar noise .... I can only make an assumption that it is the auxiliary belt or tensioner bearing, or even timing belt/chain as it sounds like resonance (e.g. echoing in a cavity) could also be amplified within the engine bay with the bonnet closed.

[SinWin]

Thanks a lot! I'll be sure to check the auxiliary belt and tensioner — though I suspect the timing belt (I think it's a belt on these models) might be more difficult to inspect. However, at least I know have some suggestions as to where I can start looking =)

[Magnet]

Hello Sindre,

My hearing is poor, so I'm not much use to you in terms of identifying the noise. If it were mine, ( and I have the same engine) then  I would remove the auxiliary belt and run it up through the revs. to see if the noise is still there. If no, them obviously it's something driven by that belt - alternator, PS pump etc. 

If it's still there, I would be thoroughly inspecting the timing belt and the tensioner and water pump as a matter of urgency,

What mileage has the car done, and do you know if the belt has been changed? If it hadn't been changed, I would be thinking seriously of changing it on an age basis. Of course, you will need to change the tensioner as well and inspect the water pump. Water pumps (strangely) are available on an exchange basis over here. If you are going to change the belt then my recommendation over here would be using - preferably an Audi kit- or only Gates as an alternative. 

Hope this may be of some help.

Kind regards,

Gareth.

[SinWin]

Hi Gareth, 

and thank you for your suggestions. Since the sound is intermittent, I find it difficult to search for the source. If I, as you suggest, remove the belt and start the engine, I'll never know if the sound is just at "pause", or if I have actually found the source? Unless, of course, the noise starts becoming constant. I could, however, remove the auxiliary belt to inspect it for any damage or defects. 

The car has done 107 000 km (66 486 miles), and I don't think the timing belt, water pump or the auxiliary belt has been changed earlier. These items are, however, due to be changed at the next service at 120 000 km, which — with my driving — would be due some time next spring. 

The car has been at the local Audi dealer for a brake change a couple of weeks ago, without them finding out anything about the noise (as it, of course, wasn't there when they had the car). 

Best regards, 

Sindre

[Magnet]

Hello Sindre,

Not sure where you obtained the recommendation for changing the timing belt at 120,000 kms, but it is of interest, since I have also taken it as this (75Kmiles). 

However, the important additional recommendation is that's it now needs to be changed more frequently so I believe on the time basis, at lower intervals of 5 years, so it's 75K miles or 5 years whichever comes FIRST and that is the important bit!  If yours hasn't been changed then it is overdue on time by what I understand, and I certainly would not delay its renewal.

Of course Sindre, my suggestion of removing the auxiliary belt will only work if you are hands on and equipped to be able to do this when the noise is present. If not, I think I would go for a cambelt and associated bits change as a matter of course and see what happens. If it helps, and you have a stethoscope, it would be worth checking the alternator and other externally driven components when you have the noise.

Hope some of this might help.

Good luck

Gareth.

[SinWin]

Hi Gareth, 

thank you, I really appreciate your help.

When I bought the car in 2014, from an Audi dealer, I was told that the timing belt (I think it's a belt on this model), water pump and auxiliary belt was to be changed at 120 000 km. The car had done 62 000 km when I bought it, and had followed every service interval until then (and I have followed them after I purchased the car). I have so far entrusted the Audi dealer to inspect and change whatever needs changing according to Audi's recommendations, and I would be surprised if they haven't changed it after so many years if the recommendation is 120 000 km OR five years. However, I cannot find any reference to a change in my invoices from the time that I've owned the car. 

Best regards, 

Sindre 

[Magnet]

Hello Sindre,

Many thanks for the reply. I'm not sure if I am really helping you very much - might be more of a question of adding more confusion! 

Selling dealers may just suggest that the cambelt does not need changing when selling a car, since the buyer may try to negotiate this into the sale if it has not been done or will need doing in the near future. Experience does show that sometimes an owner will sell a car at the time of an expensive service (say including belt changes) and the dealer takes the car in and does a less major service at the time of resale.

If it were mine Sindre, I would be ringing around some main dealers ( not where you bought it or have it service) and asking their advice on the change intervals. 

We have a 2006 1.6 which is now on 137,000 miles and the first belt was changed at around 70K ( when I  think the specified time was then 7 years) - from memory and the second change a couple of years ago at around 110K, so this has had two belts in 10 years.

It is best to talk with the service manager if possible rather than the service receptionist.

Good luck

Gareth.

[SinWin]

Hi again, 

Since my last posting here, the car has undergone a 120 000 km service, and I have had the timing belt, water pump and auxiliary belt changed. 

However, yesterday I again noticed the same grinding/grumbling sound as mentioned in my first post. It's difficult to locate, but seems to be coming from the front left side or the front middle of the car. I stopped the car, shut down the engine, and started up again a few minutes later — and the noise was gone again. 

Incidentally, the garage doing the service noted that my A/C system was completely void of gas: I haven't noticed any lack of cooling from the A/C during the summer months, so this was quite a shock to me; however I will have that checked by another workshop. I mention it here in case it might have anything to do with the noise I'm hearing: I don't think it's very likely, though, since I've been hearing the noise for over a year now. 

 

Any suggestions are greatly appreciated! 

Sindre 

[cliffcoggin]

Sindre. I can't positively identify the noise, but I echo Gareth's suggestion of using a stethoscope to listen to the bearings on the alternator and other auxiliaries. Get the type with a solid rod rather than a rubber disc like doctors use. Alternatively try a "screwdriver stethoscope" if you care to live dangerously, which is just a long screwdriver that you touch the tip to a metal part and the handle to your ear. It will amplify the noise very well but could be painful if there is much vibration.

[SinWin]

Thank you! It seems a stethoscope is the best solution, so I will try and get hold of one. 

Sindre 

[cliffcoggin]

This is the sort of thing I use:

https://www.amazon.co.uk/Silverline-154006-Mechanics-Stethoscope-320/dp/B001C0RYPG