RogerPodacter

this happens very very rarely. but when i first start the car, and the engine revs up and then the RPM's drop down, as this happens there is a sound that happens from what i assume is the flywheel or clutch plate or something. it sounds like a rattle, or like there is a loose bolt or nut vibrating, and the engine RPM's causes the loose bolt/nut to rattle in place. i hope this makes sense, its very difficult to explain.

but this only happens maybe once a week. it does not seem to matter whether the car is hot or cold. in fact it only happens when its hot because a cold start leaves the RPM's higher so the sound doesnt happen then. it happens as the RPM's are dropping down to idel speed.

this noise does not happen any other time, not while driving, nor idling, or any other time. its just when the car engine is first started.

it sounds like a circular or centrifugal force type of sound. for example as the car starts, the flywheel or some other component connected to the engine spins up with the engine, and something rattles in that system. it goes away immediately, meaning it lasts for 1 second and then stops when the engine drops down to 750 RPM idle speed. but it doesnt happen during any shifting or driving. very strange.

does anyone know what this might be? i've read the throw out bearing threads, and i don't hear any of those sounds, so i don't think it is related to that.

also this sound is not too loud, you might not always hear it unless listening for it. and it only happens once a week, or around that frequency. its not on every start. in fact it almost seems like it might be related to the WAY the engine turns over. for example sometimes the engine starts right up, while other times it might have an extra few cylinder fires and then starts up. it seems to happen more when it has the slight hesitated start up. thanks.

nbtx

two possibilities - dual mass flywheel or piston/ring clatter.

poltergeist

Could be almost anything...my first guess would be exhaust heat shield or catalyst rattle?
Often tend to go away as soon as the exhaust system begins to heat up.

RogerPodacter

Well the reason why i think its related to clutch or flywheel is the the tone of the noise seems to match the rpm drop. Its like there is a loose washer just vibrating due to the engine start up vibration or from the rotational movement of the flywheel. Don't think its related to piston or exhaust. But i'm not an expert. I also don't know that this is critical, it rarely happens.

Itchytoe

Does it sound hollow? Kinda like blowing over the top of an empty coke bottle? Mine has started to make a sound like what you described, and also very rarely. It does seem to be clutch/flywheel related too.

RogerPodacter

Yes it sounds exactly like that. From the sound of it, it does not sound like a big part making the noise. It sounds like a very tiny metal screw or washes vibrating. And like i said it seems to be directly related to the clutch or flywheel, a rotational noise. I wonder what it is.

OhNoItsMe

It could be your clutch throw-out bearing. Try this, on a cool morning, after your car has been sitting all night on a level road (not a hill). Right after your start it and the RPMs are higher, put the car in 1st or reverse and slowly release the clutch without pressing the gas pedal. The rpms are going to be high enough that the car will not stall and the car will start moving.

As you release the clutch, do you hear a sound like someone is blowing over the top of an empty bottle? Sort of like a Whooooo sound?

RogerPodacter

Nope i tried this morning and there is no such noise like that. I literally think its something like a loose bolt rattling. I don't know. Actually i haven't been hearing it lately. Very strange.