Exhaust rattling

[=Tac=]

I have an 01 T/A with A4 and 86xxx miles on it, my exhaust is rattling in the back and you can hear it in the car. It only does this is drive not netraul. Also, only when your sitting still (like at a light).

And I noticed too if the A/C is on the rattle increases a little, turn it off and it goes down?

Any ideas? Also just threw a code, P0410, secondary air injection failure. Threw this code back and December and it was my AIR system messing up. Could this be related (I was thinking if cats are clogged the AIR had burnt up again trying to force air into it, since first time code was thrown it was for the valves in the system had failed).

Thanks.

[Grims]

First step is to get under the car and see where it's loose ;)

[CKJ]

I'd recommend putting the car on either a lift that you drive up on with the ramps, or over a pit. The fact that if you put your car on a lift to lift the car up will move the rear down and take the load off of the car. You want to put it on something that will be like it was sitting on the road when its doing it. Crawl under it and give it a shake down ;) If its in a tight space, a hose clamp and aluminum foil will brace it.

[Grims]

Or, just jack it up by the axel.

[=Tac=]

Im going to be putting on some new springs in shocks this weekend so I'll be taking a peak down there. BTW, what would cause it to rattle more with the A/C on? And also only doing in gear not in neutral?

Thanks.

[CKJ]

Maybe the compressor puts more of a load on the engine at idle, causing it to idle a little lower and shake more. Motors shake more when under a strain.

[ajsfirehawk]

My 1997 is an M6 but was giving the same rattling symptom. My 19 year old gear head and I could both swear the rattle was coming from the back. It wasn't, the guts of the passenger side catalytic converter had broken up or loose and sounded like crap. Actually got worse as the car got up to temp. Swapped the cats with some high flows. Sounds better, flows better, made the code go away.

[ajsfirehawk]

So what did you find out about the rattle?