TDi Exhaust resonance hum at speed and occasional vibration? Can't figure it out...

[benelton]

Any insight or anyone with a similar issue manage to fix it.

2006 2.0TDi 140ps sportback quattro

There could be two separate issues here but I think it's related

1) more prominent when the engine is cold, there is a nasty rattle/vibration coming from the rear when tootling around with low revs in a high gear when accelerating. For example in 4th, doing about 35 ish.

i though it was an exhaust mount at first. It's a dead ringer for the exhausts rattling against something. But all the mounts are perfect, in fact the full system is in excellent shape. I then wondered about a baffle coming loose but underhand this is almost impossible from other posts I've read...

2) traveling at speed, say motorway cruising at 80, it sounds like I've got an 8inch big bore on. The resonance in the cabin is loud, accelerate to 85 and is almost gone. Take to foot off the gas and instant silence, foot back on and I have to almost shout for a passages to hear. It's worst when the engines revs are anywhere from 2k to 2.5k with the gas on.

So I though baffles again? Could it be the cat? There are no leaks, down pipe is sound, really boggled.

im told my model doesn't have a particulate filter either.

any ideas?

 

[BlueTDI]

I have exactly the same issue with mine. I think its something to do with the propshaft damping as it rotates all the time and resonates under the conditions you highlight.

http://www.audi-sport.net/vb/a3-s3-...0219-a3-2-0-tdi-quattro-prop-shaft-issue.html

 

[martinivw]

Check your rear shock absorber bushes?

 

[benelton]

Cheers fellas. After reading the post on the prop shaft, it would appear that this is my issue. The cars been in the family from 6months old and I now its been doing this for some time.

Think I'll start with the bearing and take it from there, maybe the damper if this does fix it as the whole prop seems excessive. The rattle at low speed indicates some play somewhere, hopefully this is the bearing and its the less of two (or maybe three) evils.

I wonder if this can ****** the haldex as its been doing it for so long. The car feels like it in perminant 4 wheel drive. MPG on a long would indicate the haldex is always engaged and it certainly feels that way when driven.

first thing first though, I'll get this prop issues sorted when the weather clears a bit and take it from there. maybe its worth fitting a new haldex while the props off.

The haldex has just had its oil changed at 56k and i know its never had this or the filter done previously. I asked audi to do both but they told me this model doesnt have a filter?? not sure about that, i thought they all did... not like them to miss charging for something.

 

[MyMateDaveDJ]

Same here, incredibly loud & loud vibration, then silence when over the set figure.
Let me know how you get on