[s-cars] New S6 owner / engine noise

[Eric Rechlin]

Hello everybody,

I know this is long, but I didn't want to leave anything out.

Ten days ago I purchased a 1995.5 Audi S6 Avant.  It's silver on black and has 
about 147,000 miles.  I've been looking for a car like this for two years, so 
I am happy to finally own one.  It's currently completely stock; we'll see how 
long I can keep my wallet buried.

I have been reading this list for over four years (since before the switch to 
Audifans), even though I have not had an S-car of my own.  My parents bought 
an S6 sedan in 2002, and although I rarely see it (I live on the other side of 
the country), the list has still been helpful in diagnosing problems for them.

Unfortunately, now I have a problem of my own that needs to be diagnosed.

About 24 hours after I bought the car (after which I'd driven it about 1,200 
miles, from Wisconsin to southeast Texas), I noticed a tapping noise from (or 
near) the engine, and I've been hearing it in the week and a half since.

There is no noise when the engine is idling with the clutch disengaged or the 
transmission in neutral (either when standing still or moving) -- only when 
the engine is connected to the wheels and the car is moving.

I haven't yet noticed the sound right away after I start the engine, but I 
always have been able to hear it within a couple minutes.  Even when the 
engine is plenty warm it makes the noise.

I do not know how to best describe the noise.  It is kind of like a metallic 
rubbing/tapping sound.  The frequency is directly proportional to engine 
speed, and my wild guess is that it is probably on the order of 10 taps per 
second.  I can hear it the best in the 1500-2500 rpm range.

I have yet to hear it in first gear.  It seems to make the most noise when the 
engine is not being quickly accelerated, and it is probably loudest in fifth 
gear around 40 mph.  I can usually hear it in fourth and third (and sometimes 
even second) gear as well, but it's not as pronounced then.

I have not yet found a competent Audi mechanic in Houston, or I would have had 
it looked at by now.

I searched the archives (the Audifans search feature didn't work so well, but 
I was able to search the four years of archives I have on this computer), and 
came up with a few ideas.  I checked the spark plugs, and they all seem tight 
(couldn't get them any tighter with reasonable force).  Some might say it is 
valve lifters, but it doesn't happen at idle and doesn't go away when the 
engine is all warmed up, so I don't know if it meets the criteria.  I wouldn't 
consider myself even a remotely competent mechanic, though, so I wouldn't put 
any faith in my guesses.

The oil hadn't been changed recently (it had been 8 months and 7,000 miles), 
though the previous owner had been good about maintenance, so I had the oil 
changed on Saturday (10w30 regular oil), but that didn't affect the noise. 
There's plenty of oil in the engine -- it's at the max level on the dipstick. 
I've filled up with gas (93 octane) twice in the 9 days since the noise 
started.

The good news is that the car passed inspection, including the emissions test, 
on Saturday.

The previous owner, located in Evergreen, CO, seems to have always made sure 
everything was done as needed.  They spent over $15,000 in repairs over the 
last three years, and things like the clutch, timing belt, hydraulic system, 
and engine accessories are all practically new.  I do see, however, that the 
lifters have never been replaced.

Does anybody have any suggestions?  I hope to at least have some ideas before 
I take it into a repair shop that surely knows less about the car than this 
list.

Thanks,

Eric Rechlin
1995.5 S6 Avant
1991 100 quattro