2005 Audi A6 3.2 L - 85,000k

Last few weeks, on startup - intermittent noise but more common when engine has been sitting for some period - I get a bad noise on startup for around 20 seconds.

While it is happening, the engine seems to idle a bit inconsistently but doesn't die (yet). Noise doesn't seem related to revving engine.

Location - not sure - seems more to the passenger side and closer to cabin but honestly can't pinpoint and this could be very wrong with all the covers etc.

Started it this am and got a video, you don't get the start but you get a good 20 seconds of the noise and you can hear it clearly shut off or stop at the 20+ second mark. Honestly the noise is worse in person. Very metal type sound to it.

It was in the shop two weeks ago and it didn't happen in the shop (figures), so I'd some info to help point them in the right direction. Once it clears, the car seems to run fine, but the noise at startup sounds bad.

First post, if I left something out, let me know and thank you in advance for any advice.

 

If you rev the car during that period does it go away?

The only things that come to mind based on the location you described is a cam chain tensioner issue or a lifter that isn't getting oil.

I'm new to these cars but that sounds a little too harsh for lifter noise. After seeing how the cam chain tensioner works on these when doing the oil seals though I can see it making that noise if the hydraulic tensioner isn't applying enough pressure at start up. Would sound like dragging a bike chain over the corner of a table....

So, those are my thoughts, don't jump to anything based on them though, just hoping to spawn some conversation for you.

 

Revving the engine, unscientifically, seems to get it to stop a little earlier - but it isn't automatic or even necessarily reliable. It works about as often as moving from Park to Neutral or reverse - but I'm not certain any of those are real effects as the length of noise is inconsistent.

I'm pretty ignorant but it also has had a what I thought was a bit of fuel pressure leak - I need to get in the car, turn the key to power stuff up and pause 10 sec or so before turning it over. If I do that, it starts fine. I thought that was unrelated but on reading your reply, I thought I would add it.

Overall, I would say the description you have of the chain on the corner of the table is pretty good - it is a consistent repeated metal sound until right at the finish when it pretty quickly resolves.

 

That sound is 90% coming from the cam chain. Notice how the noise goes away after a while, this means that the top of the engine isnt getting lubricated quick enough.

This is why the 3.0's have the cam lobe failures. The engine is too crowded and the oil cant get to the top quick enough.

Things that MAY* help is changing the oil to a 0 weight. M1 0w-40 and change the filter to a good brand with proper by pass valve.

Check the cam chain tensioners.

This sound is considered normal IF you have it and it goes away after 1 second. Yours is too long.