Rev Specific Rattle

[wilco184]

Hi,

I'm suffering with a really annoying rattle that seems to be rev dependant; between 1200 - 1400 RPM.

I fairly sure it's outside the cabin, possible in the engine bay. So far, I've checked that the under tray is secure, the bonnet corners are tight, the MAF sensor is not hitting the engine mount, the vacuum valves are securely attached and a general look around the engine bay; but the rattle is still there.

Does anyone have any idea what it could be? I'd love to hear if anyone has encountered anything similar.

Regards,

Matt.

 

[a2sumo]

Hi Matt my money is on the heat shield below the turbo-it protects the inboard cv joint from heat and also stops grease if it were to leak from the drive shaft gator catching fire. They are not expensive and we have had to have both out tdis covers replaced. cheers mike

 

[dan_b]

I have the exact same rpm-related issue, it does my head in. It's quite a metallic sounding vibration, but to me it sounds as if it's coming from front-left, which would rule out the turbo heat shield surely?
Bonnet latch mounting?

 

[wilco184]

Thanks for the suggestion, Mike. I have investigated the CV guard today and it seems to be intact. There is a slight movement to it if you flick the unsupported end; but I couldn't see any broken fixings etc.

After having a good look around today, I think I finally know what is causing the noise. Tony identified at the open day that the flex part of the exhaust was leaking. I have since ordered a replacement part, which should be here on Tuesday. The rattle seems to be coming from the leaking flex. The noise started sometime between Tony identifying the leak and now, I think on the way home incidentally; I don't remember it happening in MK. Although it is not a rattle itself, it sounds very similar. I'll replace the flex and hopefully the problem will be fixed.

Thanks for the help.

Matt.

 

[wilco184]

Bad news unfortunately

I've replaced the flex and the rev specific rattle is still there. I've literally no idea what else it could be. It's very specific to revs just above idle, in a band of about 200 RPM. Does anyone have any other suggestions?

Many thanks for the suggestions above.

Matt.

 

[Birchall]

Bad news unfortunately

I've replaced the flex and the rev specific rattle is still there. I've literally no idea what else it could be. It's very specific to revs just above idle, in a band of about 200 RPM. Does anyone have any other suggestions?

Many thanks for the suggestions above.

Matt.

Is the alternator centre clutch and pulley secure and not the cause?7

Steve B

 

[wilco184]

Is the alternator centre clutch and pulley secure and not the cause?7

Steve B

Thanks Steve.

I've just been looking through posts about this and the symptoms of others sound similar to mine. I'll investigate this tomorrow.

Matt.

 

[wilco184]

After some investigation, I'm still not entirely sure.

The noise definitely seems to be coming from that area, and the tensioner seems to vibrate quite a lot. (See video below) I'd really appreciate if anyone that has had similar symptoms could let me know if it was the alternator pulley.

I tried to check the pulley by trying to turn the shaft backwards and forwards, by using the splined head in the middle of the shaft. (Not the pulley spline) I couldn't move the shaft in either direction. Is this correct? I assumed not.

I should also note that my alternator had a spline socket for the shaft; M10 XZN to be exact. Skipton mentions in post 42 here (http://www.a2oc.net/forum/showthread.php?21696-Noisey-Pulley-Tensioner/page5) that it is a Torx bit. I'd recommend checking which type you have if removing, I certainly wouldn't want to be using the wrong bit and then mashing the head. See photo below.



Here is a video of the tensioner movement. It's quite hard to see due to the video frame rate, but you can see the limits of movement.



Here is a video of the noise from inside the car. It's pretty hard to hear, but you can make it out just above idle speed.



I certainly appreciate the help with this.

Matt.

 

[wilco184]

I re-checked the pulley last night as I still wasn't convinced, only this time, I removed the belt when checking. When holding the rotor still, the pulley wouldn't turn in both directions. I assume this is a definite sign of the pulley seizing? Also, with the rotor released, the pulley was harder to turn forwards than it was to turn backwards. Is this normal?

Thanks in advance.

Matt.

 

[Birchall]

the pulley was harder to turn forwards than it was to turn backwards. Is this normal?

Thanks in advance.

Matt.

The pulley clutch mechanism is designed to only engage fully in one direction so that on the overrun is does not slow down the spinning of the Alternator (I believe) so it should turn more freely in one direction (not the group)!

Steve B

 

[wilco184]

Finally fixed!

I thought I'd provide some closure to this. Steve was spot on with his suggestion of the alternator pulley, it was seized completely. I purchased a replacement pulley from my local motor factors. This was an 'INA' pulley, for £30, which is much less than an Audi replacement. I also borrowed the special tool from a friend, so this turned out to be a fairly cheap fix. With the pulley swapped over, I could tell within the first second of startup that all was well; the noise has completely gone. I've been living with the noise since the A2 Cars open day, and I'm extremely pleased that it's finally gone!

Thanks for the help.

Matt.

 

[dan_b]

I think I've discovered what my 1400RPM rattle was too.
An inspection this morning of the left-side bonnet catch and the scuttle panel underneath it revealed that the foam damping under the scuttle panel was completely shot away, and the end of the metal bonnet catch appeared to have been the cause of destroying the foam, and appeared as if it might be vibrating against the chassis underneath the windscreen.
I've stuffed the area with foam and also wrapped some foam around the end of the bonnet and, so far, fingers crossed, the noise has gone...

 

[wilco184]

That's good to hear Dan, I'm glad you've fixed the issue. I'm sure you'll agree that driving is considerably better when there's no rattles!

Matt.

 

[dan_b]

I've still got some rattles/creaks from the dash, and also one annoying one from the B pillar area, but we'll get them all, eventually!