1. When I'm driving down a city street, or a country road (20-40mph) I get what sounds like a faint flap-flap-flap. It sounds like what I have heard a wheel bearing sound like in some cars, except it is not louder when turning one way or another. I pretty much only hear it when driving in a straight line. I can't really tell where in the car it is coming from, but none of the wheel bearings have any play that I can find. It started when I put my new RS3s on and didn't remove the stickers, but those stickers are LONG gone now (500 miles and about 18 autocross runs) and the noise is still there.

2. When I am cornering very hard (autocross) I hear what sounds a little like change sliding across the metal floor of the car. Sounds like it's right under my seat. I have carpet and have checked that carpet for spare change, and there is none. The trunk is empty, glove box is empty, and I am baffled.

 

I don't know but you deserve an award for that avatar.

Don't replace wheel bearings until you have knock-back.

 

2) The very bottom of the front fender liners covers an opening into a seam/cavity underside the door sill. I've pulled remarkable amounts of leaves etc out of there before. Check there.