I’m having a vibration problem with my 2001 A6 2.7t 6-spd. It has 104k miles on it., 50k of which I’ve added since its purchase 4 years ago.
It all began in May when a serious rhythmic, speed dependent noise started emanating from the car; front driver corner location. I took it to my private shop and they diagnosed and replaced the front lower control arms and bushings. This eliminated that problem but a couple of days later, when I had occasion to be at highway speeds, I noticed a (admittedly slight) speed-dependent vibration that hadn’t been there before. I took it back to the shop and they claimed they couldn’t detect it and so couldn’t begin to diagnose it.

So I then took it to a second independent shop who confirmed it. They examined the control arm installation and found no fault with that and so blamed the tires (two were worn down pretty good, two still had adequate tread). Four new tires later, and three separate attempts at balancing them (including ‘road-force’ balancing) the vibration was still there. He even returned two of the tires on the suspicion of a defect but to no avail. He also replaced the centering adapter-rings suspecting they had become compromised. I will add here that with each successive effort at working the tire issue (be that re-balancing or replacing) the problem seemed to improve slightly, finally confining itself to between 62 and 79 mph. (though actually, I haven’t yet taken it beyond these speeds).
This second guy thought it might then need a rebuilt drive-shaft assembly since the vibration didn’t seem to be ‘in the steering wheel’ or isolated to any specific corner, but rather was that sort of ‘whole-body’ vibration that used to signal u-joint problems (in the old days). He added that the boot around the front joint had a small tear that might have allowed debris to enter and/or grease to escape, further corroborating this theory. However he then also added that it didn’t actually seem to have been compromised; i.e., it seemed tight and in good working order. Now then, using a re-manufactured assembly, this would have set me back $900+ with no assurance of success or, in the absence of success, a willingness (on the part of the shaft supplier) to take the part back. Having already replaced tires to no effect, and having little appetite to continue throwing good money at potentially unnecessary parts, I decided I ought to break down and take it to 'reputable' Audi dealer and let their ‘experts’ take a shot at it, the idea being that I could ask for no better authority than them (at $130/hr. of course).
The Audi dealer pronounced the car fit-as-a-fiddle, nearly marveling at the solid condition of the entire drive-train and suspension. “Not even a motor or transmission mount” I asked? Nope, said they; she’s as tight as they come. They didn’t even mention the tear in the front joint boot (and I had deliberately not mentioned it to see if they would find it to be a problem). “It’s those aftermarket wheels you have on the car” said they. I need mention here that in the 50k miles I’ve owned it, it has had the same set of Oettinger 17” rims it came with, and the car has never had this vibration problem before. That doesn’t mean they can’t now have a problem, but they didn’t have any such problem two months ago.

So, my fellow Audi enthusiasts, has anyone encountered such a problem and what was the remedy? Where might I look next? I’m not adverse to spending money as long as it actually solves the problem but I loathe the idea of swapping parts when nothing suggests that. At present, the car is not a ‘complete’ Audi, lacking the requisite driving refinement at highway speeds. I used to brag that the car really began to ‘settle down’ at 85 mph and above, assuming a completely stress-free composure where one could “drink tea with pinky properly extended”, and now I don’t want to drive it past 60.
Help!!

 

that was kind of a long read. seems like you and your shops have tried all the usual suspects. i must admit i'm kind of at a loss.

the audi AWD system is pretty sensitive to minute (comparitively speaking) differences in tire tread/balance/alignment. I have similar symptoms from time to time but it comes and goes.

my first question is do you notice the vibration more in your hands on the steering wheel on more in your backside through the seat?

 

Sorry about the lengthy epic but I wanted to avoid revealing all the salient bits of history one reply at a time.
There is little, if any, vibration actually transmitted through the steering wheel. It's more of that 'whole car' experience I mentioned which I guess puts it more into the back seat category.

 

sorry I haven't gotten back to this thread in a few days. Life, you know.

Anyway, I really don't have a definitive "well then its obviously the..." type answer for you. Based on your thorough description of the problem, I keep coming back to a balance issue. However, it appears that the shops you have taken it to have really done their part to make sure that it's right.

I also don't discount the Audi shop's assessment that your aftermarket wheels could be the culprit. It may be that they were vibrating "all this time" and it didn't affect your ride due to the "slop" from your old lower control arms/bushings. After replacing those, no more slop, hello vibration.

bear in mind I'm just an enthusiast, not an expert

 

Have you checked the alignment?