Strange sound from under car when engaging clutch

[BillK]

I have the 6sp manual, E90 M3, I had the dealer flush out the brake fluid recently, last week. Today, I notice a strange sound from under the car when I disengage the clutch while going really slow. It sounds like an empty can rattling under the car, almost as if a ran a can over. Its very brief, like a second or so. Any opinions?

[thekurgan]

Is it a cowbell sound? Did they also bleed the clutch along with your brake service?

[BillK]

I suppose, by a stretch, you could call it a cowbell. It sounds the same as if youre driving a couple miles per hour and then drop an empty tin can out the window. But the sound only lasts a second or so. The sound seems to come from under the engine. i'm wondering if they did bleed the clutch and in removing the lower plate cover, left something. They also changed the spark plugs and the thought of them dropping something down on the cover also crossed my mind.

[Devant]

The brake fluid also functions as the clutch fluid, if sound is indeed coming from the clutch I’d be surpised because they power bleed the fluid so there is no chance for air.

More important to note is how the clutch feels. If it is not spongy then I doubt there is air in the system that needs bleeding. You issue may be unrelated altogether.

It sounds like cowbell to me (rocks traped behind the rear brake rotor's dust shield)

[BillK]

Originally Posted by Devant

The brake fluid also functions as the clutch fluid, if sound is indeed coming from the clutch I’d be surpised because they power bleed the fluid so there is no chance for air.

More important to note is how the clutch feels. If it is not spongy then I doubt there is air in the system that needs bleeding. You issue may be unrelated altogether.

It sounds like cowbell to me (rocks traped behind the rear brake rotor's dust shield)

The clutch feels like normal. Interesting thought about rocks, but how could a rock be trapped and rattle behind the brake shield? I would assume that it might get wedged, but loose to rattle? By the way, I took the car out to the store and I didnt hear the noise again.

[Gsv77]

It is definitely a rock behind a brake shield. Sounds like dragging tin cans...has happened twice to me before. Take the wheel off and a pebble will fall right out.

[BillK]

You're probably right. I didnt do anything and the sound just went away by itself. the rock must have fallen out