Door Vibration Noise

I use a Galaxy 2013 diesel as a taxi. On Saturday 27th October, a vibration humming noise (a bit like a bee in a container) started in an area around the front lower, front passenger door. It`s a bit like a loose screw or something metallic in one of the air ducts. I checked all these and they are clean.  The noise increases and decreases according to the revs at the time. It really is annoying as I am in the car most of the day. I yhave checked all that I can without removing the internal door panel which is probably my next step. Also, I found two of these items laying loose on the vehicle floor. One in the front passenger footwell and one directly behind it in the rear passenger footspace. They are made of a flexible plastic material and measure about 2" by 2". Can anyone help?