Diagnostic experts - what's the rattling I hear?
 

Weird noise - car has been doing it for a while. Here are the symptoms as I can best describe them:

Intermittantly I'll get a rattling noise (sounds an AWFUL lot like a heat shield, but I checked and they all appear to be tight). It seems to happen only when the car is warm (operating temperature, running a while) not when cold. It also is much more prevalent when the car is juuuuuust starting to build boost - as I'm building it, the noise will happen just as the boost gauge swings through the 1.0 - 1.2 ish range, then usually disappear.

I don't think it's really hurting anything (seems to be running okay - no other symptoms).

It's just annoying as the noise is one that can occur with some regularity even with "normal" street driving - I don't have to be really romping on it to have it happen.

I got under the car and shook the heat shields and pipes - nothing obvious. Maybe it's that enormous catylitic heat shield, but all the bolts are there and it seems pretty secure - maybe it's heating up and expanding or something?

I had a car with almost the same symptoms and the headers were cracked.

same thing happened to me and the starter heat shield cracked the bolts were tight but it had a huge crack in it.

Are you sure the engine is not leaning out (running lean) as boost builds? That "rattle" could be detonation (ping, knock).

Pretty sure it's not leaning out. If anything I suspect it's a little on the rich side. People on drives behind me say that I shoot a little bit of black soot under heavy load, so I'm fairly certain that's not it.

How would I check the headers? I inspected them visually but see nothing wrong.

I'll check all the heat shields again.

Check your engine oil for metal shavings. My "rattle" came at a certain RPM and turned out to be rod bearings a couple of years ago.
-R.B.

Scary thought. . .

Nope I'm fairly certain it isn't that. I just changed the oil last week and although it was dirty (I'd waited a bit too long) there was no metal in it (thankfully).

A catalytic converter that's breaking apart (due to age) will sound like a rattle. In my case though it's heard more at idle than at a specific power band, but I certainly could see an increase in exhaust gasses causing some type of harmonic turbulance in there.