It's a rattle and is is coming from behind the drivers side. If I open the door and lean out I can hear it coming from the wheel area. It only occurs when the car is in motion, under power or not. In gear or not, and clutch engaged or not. It's been there for a while but I think it's getting worse.

You may have to turn the volume up to really hear it

 

Try lightly applying brake while going at speed with active noise. Does it stop? If so, add some brake pad paste and make sure the clips are tight. If it is not brake related try a Gopro under the car to see if wind is moving trim or belly pans.

 

I'll try the brakes. The gopro is a great idea! I don't have one but it is clever