My car makes a rattling / clattering sound in the exhaust. It makes this noise when I let off of the throttle, or if I coast/decelerate with the car in gear. From under the car it sounds like it is coming from inside the downpipe. From the engine compartment it sounds like it is coming from the turbo area & under the car. I assumed that it was a loose heat shield but everything seems snug. I don't think it is an exhaust leak since I think I would notice that more on acceleration as well. It has made this noise for quite some time but it has gotten progressively louder or I have become much more sensitive to it. I first noticed it after replacing my lim gasket and installing my n-tech downpipe which is much thinner walled then the pre-cat. Could this be my waste-gate flapping? That's what it sounds like, a valve or butterfly flapping, clattering, rattling, god, I'm getting annoyed just thinking about it. My boost seems to be smooth. If you have any suggestions please let me have them.

 

to me it sounds like your cat has gone bad. i had a similar sounding problem. do you have a boost gauge, if so what is your secondary boost number, if its the cat then the secondary is probably low. i would check that first. a way you may be able to pinpoint it more is get a garden hose and cut about 5 feet off of it, (or similar hose) then crank up car, put one end up to the cat and other to your ear, move it around and you will hear it is more then likely the cat, good luck, scott

 

Probably a piece of your cat rattling around.

 

My secondary boost appears to be fine ~10psi. I have a PFC though, maybe it is compensating somehow and smoothing it out??? I will pull the cat off and check it out. Any other suggestions???

 

Its your cat. Mine does the same thing. Either get a new high flow cat or a midpipe. I hate pulling up at a drive through with the ..clankity clank clank.

 

yeah, it's embarrassing to pull into a parking lot. I try to push the clutch in to prevent the rattling. I'll have to try to take care of it soon. I'll probably take it off and try to clean out any loose pieces for now and look into replacing it. Thanks, I'll keep you posted to what I find.

 

Well, I finally fixed the rattling. It turned out to be one of the actuator rods not pushing one of the exhaust flaps in the exhaust manifold closed all the way. A lot of people seemed to have the very bottom one come loose and rattle, the turbo control actuator I believe, but the one that was loose on mine was the middle one, the one with the bent shaft. I think it is the pre-control actuator, but not sure. I just hosed down the rusted/threaded lug on the end with some wd40, then held the shaft with one pair of pliers, and turned the lug on 1/2 turn tighter. A pair of vice grip pliers would have come in handy to hold the shaft. Just turn it in enough so that you have to pull the shaft out of the actuator a little to get it to slip back over the rod with the eclip. It's nice not hearing that annoying rattling everytime I'm coasting in gear :-) Thanks to everyone who helped me with this.