Just so we're clear: The sound OP is talking about is NOT the start-up-dance backfire lump.

I listened extra hard today. It does sound like it's coming from the flywheel area, and comes and go with the clutch in/out

Cars with automatic trans do the same thing. You might notice that if you put the car into gear, push in the clutch, or otherwise get rolling it goes away immediately. I've been told by several tuners that the noisy startup is due to the way the car tries to heat up the catalytic converter. There isn't much they can do to change the startup sequence.

than why does the sound go away when the clutch is pushed in? what does the clutch have to do with the catalytic converter?

Happened to me few times when it was extremely cold. The engine would make bap bap sound for 2-3 times and it goes away after it warms up. Never happens during warm weather.

It's not the cat that's making the sound. My car has no cat in the header and it makes the same loud cut-out sound. It's the startup fueling. The car starts up with TONS of negative timing until the car warms up. When I bump my automatic into drive it seems to bypass that noisy startup sequence and go straight to the 'warmed-up' idle of ~750 rpm. If people with manual trans are reporting pushing in the clutch does the same, it's probably because the ECU is detecting the driver is wanting to get rolling.

I've chatted with a few tuners about startup and this is my best guess as to what's going on. I can reproduce it just about every time I start up when it's under 40F out IFF I just let the car idle to warm-up. If I go into gear a few seconds after start-up, the revs immediately drop and the car smooths out.

Wow glad I found this thread..

I just recently turbo'd my car so I have been paying extra close attention to every little noise the car makes.

I heard this at idle and was getting worried.. but it goes away as soon as there is any load on the engine.

I had my tuner raise my idle a tiny bit and now it doesn't do it at idle, but it still does it when I give the gas pedal the tiniest little tap. The car wants to studder and then "knock".

I have a hunch it is something to do with the idle/not under load timing.. or piston slap... but whyy..

you must have changed the clutch since you turbo'd your car, but did you by any chance change the flywheel?

yes, and no the noise I am talking about isn't the flywheel - that definitely makes it's own rattle

Also glad i found this thread, we have been having cold mornings in houston as of late and my car started making this noise. First i thought it was rod knock but realized it wasnt following RPM. My guess is it has something to do with the engine rocking/shaking when it hasnt warmed up yet. I first noticed it after adding the positive shift bushing into my transmission, but not sure if this is related.

Mine was definitely flywheel/clutch rattle. Goes away with the clutch pushed in.

ya your right, i heard it again this morning and i realized it wasn't coming from the engine. i listened carefully and noticed it was coming from the transmission, specifically right where the transmission mounts on the engine. I have a feeling that it may be the release bearing or the fork rattling, and once the clutch is engaged and the bearing makes contact with the pressure plate it stabilizes, but thats just a guess :iono:

1800 miles on the clock, and heard it the first time today.

Mine matches the noise from the outside in the second video DEAD-on.

6-spd manual, but other posters were saying they were hearing it on the auto as well.

I was also having idle hunt a little more than usual as well. Nothing to bring it to shudders or throw a code/light, but just varied a bit more.

-Rich H.

So my first BRZ was totaled and I got a new one in March, and this one doesn't make the sound.... hmmmm