I posted this on A6 section, but wanted to get more input. So I post it here as well. I have an 2001 A6 Avant quattro with 2.8L and tip. I have been hearing this clunking noise from the engine bay for awhile. It came and went, and I even took it to 2 different mechanics. At the times, theywere not able to hear the noise.Now the noise is definitely permanent and I wanted to pick everyone's brain about the noise, before I take it in for a check. There is no fault code on any sort.

I went under the car and checked for any noticeble deficiencies aweek ago. The only thing I noticed was that the front passenger side transaxle had a bit of play in it where it went into the transmission. Interestingly enough, when I turned the transaxle back and forth for a few times, the noise dissapeared for awhile. Not it is back again. It is mechanical clunking noise, and almost sounds like bad CV joint. I know that the inner CV joint sometimes goes bad, but I didn't really notice any play vertically.

So what do you think? Is it my tranny? Or differential? Can I replace the defferential by itself without replacing the whold tranny? Any similar experiences? Any inputs are appreciated.

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2001 A6 Avant
2.8 ATQ, Quattro, Tiptronic
Mods - SpeedTuning Chip, K&N
Repairs - Too many to list! And you wonder why I still drive an Audi

so its a 2.8 auto tranny and does the noise only happen on cornering? if yes its a CV joint/boot

Yes on 2.8 and auto tranny, but No on noise only on cornering... Noise is constant whether it is going straight or turning. It is more noticible at low speed around start to 40 mph, but it gets covered up at higher speed. But I think it is still there, just that it is masked by other noises.

I checked for the play in outer CV joints, and they are tight. Also boots are in good shape. Any other suggestions?

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2001 A6 Avant
2.8 ATQ, Quattro, Tiptronic
Mods - SpeedTuning Chip, K&N
Repairs - Too many to list! And you wonder why I still drive an Audi

have you checked all the mounts, motor/tranny? loose crossmember? check to make sure the bolts holding in the axel are tight.

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"You a bounty hunter? A man's got to do somthin for a livin these days.... Dyin ain't much of a livin boy."

Mounts are tight as well as all the bolts...

I am dreading taking the car in hoping that it is something not major.

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2001 A6 Avant
2.8 ATQ, Quattro, Tiptronic
Mods - SpeedTuning Chip, K&N
Repairs - Too many to list! And you wonder why I still drive an Audi

is the noise on when moving or shifting, if its on shifting i can almost gauantee that its the tranny mounts, you cant tell of the tranny mounts are bad until you remove them. i had almost the same thing as you described when shifting and when i pulled the mounts one was ok but the other fell apart in my hand.

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An audi without quattro is just a VW

Shifting does not make any difference. FYI, it shifts like butter as all audi tips do. It is a clicking/knocking noise that is constant in sense of always, but irregular in interval. As in, it is no clunk, clunk, clunk, but rather clunk...clunk.clunk...clunkclunk...clunk, without any rhythm.

I will take the car in next week when I can borrow another car for communte purpose. But meantime any other suggestions/ideas welcome.

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2001 A6 Avant
2.8 ATQ, Quattro, Tiptronic
Mods - SpeedTuning Chip, K&N
Repairs - Too many to list! And you wonder why I still drive an Audi