[ikenjoku7]

Can someone tell me what this is? It happens anytime I go above 40 after first starting up my car but usually goes away after a while. I got no check engine codes or loss of power

[ikenjoku7]

Here's a video.

I get this weird rattling noise whenever I accelerate past 40. The sound noise goes in and out and goes away after I drive for a while. I was told that it could be something loose in with my exhaust but the guy who told me that didn't seem like he knew much about our cars (a guy from advanced auto parts) and he just gave me a general idea on what he thought it was.

[tadaska]

I believe this sound is called flapping

[Fundguy1]

Blown cats? Have someone drive next to you and try to figure out about where it's coming from.

[fravel]

Check the paneling on the underside of the car, I'd bet one of them is loose.

[Volasko]

The frequency of the flapping noise makes me believe its driveline related. Something hitting a spinning part. Strange how it only happens at speed.

[Fundguy1]

I would say the underbelly pabelieve is loose but it should happen regardless of acceleration or maintaining speed it that was it.

[trjn]

Is that sound from interior or exterior of the car?
Make sure there is nothing fallen inside the blower motor cavity. You can reach there by removing cabin air filter.
I had similar noise, turned out the dealership dropped a plastic piece(must have broken off from somewhere in my car when they replaced the filter) in there and it would only make noise in certain car speed and full fan speed. Worth a check, because that was the cause of very similar noise in my car.

[ikenjoku7]

It's coming only from the inside of my car. I removed my cabin air filter and reached in to see if I could feel anything but I feel nothing

[ikenjoku7]

My car still makes that noise with the fan on or off and now the sound doesn't go away after a while. I'm gonna take it to a shop to see what they think it could be. Any shops you guys recommend in the Atlanta area?

[Wilt]

You gotta MT?...when you get up to rattling speed, push in the clutch and let the engine drop to idle...that lets you know if perhaps it is a rattle related to engine speed.

If the rattle continues in spite of engine speed dropping, then perhaps it is the driveline related rattle, so listen for rattle to cease as car coasts slower.

[ikenjoku7]

Originally Posted by Wilt

You gotta MT?...when you get up to rattling speed, push in the clutch and let the engine drop to idle...that lets you know if perhaps it is a rattle related to engine speed.

If the rattle continues in spite of engine speed dropping, then perhaps it is the driveline related rattle, so listen for rattle to cease as car coasts slower.

Mines automatic but I know that whatever it is it's something spinning and the same sound doesn't happen at the same time like it would if it was a broken fan. The noise has an irregular pattern like you can tell it's something being thrown around on there. Like a coin in a dryer. And it happens when I only go past 40 mph. It occurs a little slowly once it hits the low 40s but by the time it hits 45 it goes crazy. So it has to be something electric powered that turns on only at speed. Any ideas?

[atc1009]

Any updates on this? My 2011 335i started doing this the other day. For me it occurs around 2400 rpm though will also sometimes randomly pop up. At idle there is zero rattling noise. It isn't connected to the speed of the car though as I've had it occur while stopped and revving the engine. Any input is helpful before I take it in to get looked at

[Sco Cuddie]

This similar noise occurred in my previous e39. Ended up being a shot exhaust mount and the exhaust would bounce on the center support.

[Efthreeoh]

It's almost useless to try and diagnose sounds over the internet, but my best guess, and as others have suggested, the noise is one of the underpanels is loose and flapping at speed.

[atc1009]

Originally Posted by Efthreeoh

It's almost useless to try and diagnose sounds over the internet, but my best guess, and as others have suggested, the noise is one of the underpanels is loose and flapping at speed.

The issue with mine is that I've been able to get the noise to occur while parked and revving the engine

[Efthreeoh]

Originally Posted by atc1009

The issue with mine is that I've been able to get the noise to occur while parked and revving the engine

Then it's an exhaust issue most likely.