Strange rattle / flapping noise at highway speed
 

Hello, I've been trying different searches for similar issues but didn't see anything that seems related.

Wife's car has been great. The noise I'm getting shows no signs of being related to a poor running condition. Tires are new. Ride is perfectly smooth etc.
I believe it's a problem with the body somewhere - must be exterior.
Basically, at about 50+ mph I get this faint rattle or vibration on the left side. I've tried to localize it, but can't tell for sure where it's coming from.
It seems like it could be the door, toward the hinge, or possibly the kick panel area.
During a recent drive it even seemed like it could even be the wheel well (like the liner flapping against the fender or something like that.

Naturally, when it's sitting still I'm unable to detect anything.

I'm guessing this is an isolated problem, but I thought I'd put it out here to see if anyone has dealt with something similar.

Check the large palstic tray under the engine. I had exactly the same thing.

It's not installed, but I could imagine it could make this type of noise.

How about the smaller shield before the larger one that is missing? I believe they call it radiator splash shield.

There are wheel well liners and plastic covers on the sides too. If any of them are loose, they'll make noise at speed. When it first happened on my car, I thought that something broke. If they seem to fit and don't need fasteners then a little "gorilla tape" to hold them together will help, especially towards the front of the car where the air rushes in. With mine on the driver's side I had to tape the rear of the wheel well cover to the front of the plastic cover on the side of the car to keep them from flapping around.

To add to the "anything plastic " list is also the plastic shield for the wipers and cowl that are in the engine compartment. Had the same symptoms, and it wound up being a series of plastic rivets (1/2" Ford replacements from Auto Zone fixes this) that were broken off, but put back in place when cabin filter was replaced.

So, check this, the radiator splash shield, or anything using those plastic rivets. If it moves and it shouldn't, you have the answer.