Snow tire questions

Just bought snow tires for my 99 Camry. I have never owned snow tires before or driven in a car with them in use. These tires are called Goodyear Ultra Grip and I have 4 on the car. Two questions:

First, is it true that snow tires will effect a cars gas mileage. Mine seems to have dropped since I changed to the new tires. How much of a drop in gas mileage can snow tires cause?

Second, why do they cause such a loud whirling noise inside the car when they only contact the road at the very bottom of the tire? When I had my all season tires on I couldn't hear any noise from the tires at all.

Thank you,
Bill