arjun90

I have "Occasional" Idle Noise When Starting Up a 2004 Audi A6 C5 Avant 3.0L (143,200 Miles); usually occurs within the first several seconds of startup if the car has not been running for eight or more hours. This vehicle is driven roughly 60 miles every day.

Not sure what is causing this, but I recently changed over to Mobil-1 0W-40 Synthetic Oil from Conventional Castrol GTX 5W-30, and prior to this oil change, the sound was more pronounced; now the noise still occurs, but minimally, and sometimes never. During the Winter Months, the sound was more consistent. Note however, the sound never occurs while driving; only during the first several seconds of starting up the engine, and first couple of seconds of putting the gear in reverse.

Existing Problems in the Engine are the Spark Plugs / Ignition Coils, not sure if this could be related.

Here is a clip exhibiting the noise. Thanks

blink

Is it a rattle? Like a chain on metal?

jcman

No cam chains on a 3.0

jcman

All 3.0's have a slight clacking on start-up at least mine did until I starting using Shell Rotella T "Pure Stock Synthetic" and real good filters like Mann or Mahle and the results diminished down to no clatter or very minimal, the key to the oil filter is the drain back valve that holds a column of oil for positive pressure on start-up.

Again, like I said before recording engine sounds are not a good example for any one to diagnose unless it's blatantly obvious what is heard, I have no info on what you are using as a mic, what the sample rate is, what the dynamic range is, where it's placed and plus I'm not there.

jcman

If I recorded me playing my SRV Stratocaster on my 65 Twin Reverb amp and played "Scuttle Buttin" with my cell phone you will not hear if I'm out of tune or if a 6L6GC tube is crapping out let alone the tone that I will hear and you won't.

Stevie Ray Vaughan enters the Rock Hall of Fame!
About time, had to add that...sorry.

blink

Ah, that rules that out.

arjun90

I remember on one of the Audi forums, there was a very long thread discussing the same you are describing, but this was pertaining to another Audi Model, I believe the B4. I used the Genuine Audi Oil Filter and Mobil 0W-40 in my recent Oil Change, though it did bring the frequency of this noise down a notch, the noise still occurs occasionally, but not everyday.

I have a good Voice Recorder, but not sure if that would clarify the sound much. I recorded the video using a Samsung Galaxy Note 4, a dual-mic featured phone which I would suspect has better voice recording capabilities than my stand-alone Olympus Voice Recorder, haha.

I should use a stethoscope, just to make sure I don't hear anything deviating from the norm. The sound has been present over a year since I got the vehicle, by now a pulley or tensioner would have given in, after driving plus 10,000 miles in over a year.

What you described, is extremely accurate. Not sure if the A6 C5 Avant's, particularly the 3.0L were positively perceived.

pr0xZen

I suggest you either get a helping hand, or rig up the camera/mic so you can record from the front with hood open. It should be a small task, but it'd at least be of more help than this snippet.

arjun90

Will do, I noticed the sound is slightly present when keeping the gas pedal pressed at 1,000 RPM. Might be able to replicate the sound then.