New Cold Start ?

Fuel issues aside, when it is real cold outside and I get in and turn the key it makes a noise that i can only describe as a buzzing noise. the noise lasts a second and then usually it starts on the next 1 or 2 tries. Is this a starter problem or is it just due to the car being cold? It was nearly 20 degrees below last night with the windchill. It doesn't seem like a big problem because it always starts but I'm wondering if that "zzz" sound is anything to worry about. Sorry for all the cold start questions lately. And, Thanks to all for the help you've given me so far!

Leo