Name of noises the voice makes while singing?

I don't know if anyone else notices this, but a lot of mainstream singers these days make certain noises when they sing that sound like moaning, popping, and cracking of their voices. Some of examples of singers that do this are Britney Spears (she makes these noises a million times in her songs, especially in "Don't Let Me Be The Last To Know"), Christina Aguilera, Stacie Orrico, Fergie, Kelly Clarkson, Avril Lavigne, and about 99% of pop artists. Many people make the same noises while speaking. Is there a certain name for these sounds, what causes people to make these sounds, and does anyone find these sounds attractive?