I've got one that's stumping me. About a week ago I started up the car and as the AC kicked on it sounded like a piece of paper was rattling in the duct work. When I turned off the air, the noise seemed to go away. I was surprised when I popped the hood that turning off the HVAC didn't actually stop the noise, it just kept it from entering the passenger compartment. Even with the hood open, it sounds like a piece of paper rapidly flapping in a breeze (perhaps actually a thin metal rattling). Looking under the hood from top and bottom, and can't find a cause or sure source - it sounds like it's coming from the center of the hood / engine, but it's hard to tell. I pulled the air intake and filter and they're both clear.

Anyone run across this or have a suggested next step?

 

Another chapter in "find that noise".

Look around the drive belt and make sure nothing is amiss there.

I know it sounds like it's coming from the top middle of the engine, but check underneath the car. I had a sound last week that made me think the primary chains we about to come off and lunch the motor. Turns out it was a small tree limb stuck in the exhaust under the driver's position. Still not sure why that sounded so metallic.

 

Does the sound seem to vary with the engine RPMs ?

 

Is the noise there both when stationary and when moving?

If it's only there when you're moving, check the Undertray (item 6) is securely attached:



It's held on with 'scrivets' (plastic rivets) and oscillates making a strange noise if some of these are missing or broken.

Graham

 

Thanks for the great suggestions. Based on the advice I went out to the garage to dig around and continue my hunt. I was surprised to find the rattle had mysteriously disappeared. For now I'm filling this one under "It's better to be lucky than good."

 

I had a 'paper flapping noise' on my Transit van and it turned out to be the windscreen wipers lifting off the screen at high speed.