I have a Dreaded 3.2 Rattle of Mystery. I've done a lot of searching...

[primelens]

Hi!
Long time lurker, first time poster.

Thanks to everyone for creating such an killer resource - I've found so much information to save time and money here it's incredible.

My Audi is a 2008 S-Line 3.2 A6, bought at 62k from 1 PO, now at 93k.
Dealer serviced until 80k when I started getting serious about working on cars.
1 neglected oil change (9300 miles between).

My other car is a 1969 Toyota FJ40 expedition truck with a swapped in performance-IP'd Mercedes OM606 (1998) BiTurbodiesel (Custom compound turbos) that makes it roll forward. I did the engine swap, turbo system design, and everything else in my driveway, in the Oregon rain.

I say this only to emphasize that I have NO idea what I'm doing working on my beloved A6, and honestly little idea working on my truck (no sweet indoor shop, just a dream and a deadline) - it was all done based on conversations with fellow enthusiasts (nutbars?) and giving stuff a try - but I'm willing to get greasy!

I'm excited to enter the world of the ComputerCar, RossTech in hand. I am a systems designer for my day job; Familiar with our future robot overlords and how to listen to them.

So hat in hand, I come to the Forum with a Dreaded Rattle. I have searched, and searched, and if I missed something please point it out to me - you can even use all caps. I'll take it.

Read/watched LOTS on audi rattles, timing chain scariness to keep me up a night, but nothing that quite fits. Here is what I have:

- It occurs ONLY on acceleration, and varies in volume with the load on the engine.
- You CANNOT make the noise in neutral. Vroomyvroom vroomy vroooooooooom... People look at me, I'm just trying to perform Stoplight Diagnostics...
- It is a tdicktdicktdicktdicktdicktdicktdick as if you stick your tongue against your top teeth and make a tdicktdicktdicktdicktdicktdicktdick noise. I'm trying to get a recording, it's not as easy as I'd hoped....
- It is intermittent but in phases: Drive a few dozen miles, hearing it a little. Then it gets worse for a while, then better.
- It occurs between 1.5k and 3.5k rpm depending on gear.
- It does not affect power.
- It does not seem to become louder with the windows down (if anything, it's harder to hear).
- It does not appear to increase in tempo with RPM, but I have a hard time saying that with total certainty.

Also:
The engine is NOT throwing codes that I have read would be consistent with serious timing chain stretch. (Cam position sensors, etc).

It does occasionally (monthly) throw a code for a small evap leak, and an intermittently stuck intake flap/vane/thing.
Sorry, can't remember the codes, happy to supply if relevant.

As a result of seeing those codes, I followed AudiBug's wonderful DIY thread on carbon buildup inspection. Ta da! I have carbon buildup! Gaskets and supplies to remedy on the way...

I have run the test with the RossTech for the knock sensors. Both fore and aft are functioning, none are hitting what I understand to be the 12 degree limit. 7, however, is not unusual on some cylinders.

I recently did the Transmission Fluid Swap of Misery. Blauparts kit, whole nine yards. What a vomitously ornate process, especially leveling without a lift. Lifetime fluid *horrible swearing*. I think I bought it with the trans under-filled (CPO my *horrible swearing*) - shifts so much Mo'Betta now. On completion of this process, the Rattle abated for a while (50 miles of excited driving), then returned. I do not know/think this is necessarily related to cause, just trying to provide variables.

As a result, I am thinking:

-It is not detonation, since the knock sensors are active and not hitting limits. Maybe this is more hoping than thinking, but none of the codes would indicate detonation or mistiming. Cold starts are SLIGHTLY longer, but I'm using an aftermarket battery that's not the best (bought before I knew better, but working OK and I'll hang on to my 300 bones, thanks.)
- It is either an exhaust rattle (checked the heat shields all the way back, looked for other loose bits) or SOMETHING TERRIBLY WRONG WITH MY ENGINE, that is not detonation.

tl;dr - My engine makes a rattle when you push the skinny peddle but none of the normal (google documented) reasons check out so it's either something dumb and safe or something grim. Car in not an optional vehicle (DD).

Thoughts?

Thanks so much for reading all this - I can't afford to explode my car, your time is appreciated.

*gn

[Up2DTime]

Great detail in what's going on, unfortunately I can't help you much in identifying the mystery rattle as you've covered my suggestions. I do have a couple questions and comments, I have the same vehicle except with 180k (bought with 170k) and although I haven't had any real problems reading these kind of threads make me hesitant to do any modding. I get an Evap leak code every once in a while which I traced to my gas cap and a slight surging sometimes between 1500-2000 rpms. Did you have any negative side effects from changing the transmission fluid? Can you tell which side the rattle is coming from?


Sent from my iPhone using Audizine

[rdauer26]

I honestly would not worry about it too much. I also have a 2008 S-Line 3.2 A6 and a 2000 BMW 540i Sport. The rattles these engines give off between the two is mind boggling but more than likely normal. I recently just did the timing chain and guides on the BMW and it still rattles. Our 3.2s are damn near bulletproof besides carbon buildup and timing guides which anyone should plan to do anyway down the road of ownership. If you're not throwing any codes and it does not affect performance than I would let it be. Its just German engineering at its finest.

[c@@kieMonsta]

FYI 9300 miles between an oil change is not neglect unless you use sub-par oil and absolutely abuse the car.

[se.farrell]

I have literally the same car, so i'm sub'd for interest.

Since you mention the engine a lot, I assume the sound is comng from the front of the car? Can you tell which side of the car?
Are you sure its the engine? These cars do make a lot of ticking for someone new to an Audi (it's a little disconcerting).

I hear a similar noise, but mine;
is VERY quiet. Can only hear with no music on
It happens in about the same RPM range, but when I am in a gear higher than I should be, ie. ~28-38mph in third gear.
Mine MAY increase in temp w/ rpm (cant remember)
I THINK my sound is coming from front passenger, cannot pinpoint exactly (see below).

I was thinking CV Joint of Wheel Bearing.
The only accident my car has been in was hitting a curb when swerving to avoid being hit (sub 25mph).

[primelens]

Hi All,
Thanks for the responses. Various Replies:

Up2DTime:
No, no negative effects from the trans fluid change.

rdauer26:
Thanks for weighing in! Seems like the consensus is that nothing grim is going on. I'd still like to find/fix the noise - maybe I'm off base, but it kinda dampens the joy of the otherwise smooth, quiet, lovely car.
But then, wouldn't we all like to find/fix our mystery problems for the same reason?

c@@kieMonsta:
Thanks - I'd heard some folks felt 5k was nesessary. I only use the good stuff, and don't always drive like a maniac.

se.farrell:
Pinpointing the sound is bloody hard, since it won't do it unless the car is driving and under load, and rolling down the windows makes it harder to hear. I feel like this is a clue, however. I'm assuming it's the engine, cuz that's the scariest part, but that may not be right. I don't know if it's left, right, front or back.

They DO indeed make a lot of ticking. I don't have any basis for comparison having not owned or examined another, but it's nice to know that some of that racket is nominal.

I *think* the noise tends to get worse once the car has heat-soaked a bit.

With music on, you can't hear it, so I guess mine counts as quiet, as well.

Pure ignorance here - not sure how a wheel CV joint would create load-sensitive noise? Wheel based noise would certainly satisfy why it only occurs in motion....

Cheers,
*gn

[c@@kieMonsta]

c@@kieMonsta:
Thanks - I'd heard some folks felt 5k was nesessary. I only use the good stuff, and don't always drive like a maniac.


Cheers,
*gn

I've that too and those guys are just paranoid. Modern quality oil doesn't break down like the old stuff used to. I've had 4 Audis and I always changed the oil ever 10k miles or once a year, whichever came first. Never had any issues.

[rdauer26]

The ticking is completely normal. I got my 08 with 56k on the clock and since my ownership have only pumped 93 octane into her and change the oil every 10k with Pentosin HP II 5w-40. I will also toss Techron into the tank every 6 months.

I do the same routine for the BMW but change at 5k intervals as I just clocked over 200k on it.

Try that oil out next time you have to do a change. Maybe it will correct your random tick.