Hi guys,

I have a 2008.5 Audi A4 2L quattro 6M, ~12500 miles on it and here's the problem with it: there's a dense rattling noise coming from the engine bay, not very loud but still very distinguishable when the engine is under load and accelerating (that's when is more audible). There's absolutely no noise when engine's idle or braking (as in engine brake).

I've been to the dealer (Desert Audi, Las Vegas) and the guy said could and should be the diverter valve. Next step was to schedule the appointment, they replaced it (or so they say) and I suspect the car it did run fine (that is, no distinguishable noise) for about 30-60 min.

Overall, the acceleration is not so great as it's been, but the torque is still in place and pulling as it should. But I was surprised to find out that even a 2004 Corolla was peppier than mine at the red light. If I floor it, I might get some more juice out of it but the noise says there's nothing good going on under the hood. So, I'm being gentle with it as much as I can.

Can you tell me what it could possibly be? Also, are there any ball bearings inside the turbine that could create that noise?

Thanks

 

I think I kinda figured out what the problem is. The sound is the vacuum trying to suck more air so basically the turbo system doesn't breath too well. In support of my theory I have several points:
- the car runs hesitantly at low speeds, in 1st and/or 2nd gear, especially when I take my foot off the gas entering into the engine break phase. It frequently jerks and i have to be careful with it not to have it stalled.
- the sounds is even more audible when the engine is cold, the air/fuel mixture is too fuel rich, that's when it needs as much air as possible more than ever.
- the above point is sustained also by the numbers the guy from the dealership read for the air/fuel trim - 7% - don't ask me what it means, he said is within parameters but it was a lil bit on the fuel rich side. The max admissible he said is 10%.

I'm gonna go again to the dealership to ask him again about those numbers and what they mean.

Let me know if you experienced any vacuum sound made by the turbine try to suck more air into the system or anything alike.
Thanks.

 

Only noise i hear is the Intake. Other then that i wouldn't know what to tell you.

 

first thing i thought off the bat was the dv bladder is cracked....but that would kill your torque and cuase a very noticiable whitsle sound while the car is boosting up,

comparing the a4 to the corrolla the corrolla will always be peppier given that its not a forced induction car (i think? i dunno much about corrolla's) so the reason its not as peppy is because from 800-2700rpms your car is in the process of spooling up the turbo which gives any turbo charged car that back in the seat feeling once proper boost is achieved

the intake manifold is designed to breathe better then most intakes because the turbo needs a reletively free flowing intake to run properly....

other suggestions would be to check ur air filter both the telephone book sized air filter that came with your car and the tiny mesh filter that stops things like sand and whatnot from getting into your car (you'll run into the little guy before u get the big guy)



i'm a little confused about the issue with 1st and 2nd gear tho what exactly goes on?

 

Of course, the air filter was part of the problem. I just bought a K&N and oh boy, my car just go new wings. From the low speed/1-2 gears hesitations now begs me to give her pedal to the metal.

Now, to explain the filter thing. Personally, I didn't change the air filter at all since I bought the car. I bought that stealership maintenance crap and I was expecting for them to replace the filter at the 5k scheduled maintenance (my car has now ~13150 miles). At this moment, I have no way to verify if they did or not, however, the stock air filter looks really dusty.
On top of that, I had to take out one or two dead leaves from the pre-air filter section of the intake. That must be the reason for the car hesitations.

I guess I should pay more attention to what those dudes are doing and probably I should never trust them too much.

On the down side though, the noise is still there, it just moved from 2k-2.5 rpms to 2.6k-2.9k rpms.

 

Do you have an example how is that noise suppose to sound? Something like short description or even a sound clip if it's possible.
I keep insisting on the noise because I'm pretty much convinced that I didn't have it when the car was just off the dealership lot and 3-4 months after.
Thanks.

 

The answer for those hesitation is those dead leaves on the pre-filtering area. Not enough air.

 

yea the noise ur hearing is defineltly the intake of ur car and possibly the turbo spooling up

the reason it jumped from 2-25 to 26-29k rpms is becuase the initially the leaves were cuasing the noise and now at 26-29 ur turbo is creating a forced induction of air....its actually audible from 26-6k but after the engine hits 3000 rpm's the engines noise drowns out the intake whooshing