Hello and welcome to the forums
Which of the camera's modes are you using to photograph the night sky? Also, what is the ISO setting? A very high ISO setting will result in a lot of noise in Live View... and if you're using an automatic or semi-automatic mode for shooting, the camera may be pushing the ISO setting to a very high level.
It would be immensely helpful if you could take a JPEG photo and upload it here - not so much for us to look at the photo itself, but so we can examine the EXIF data contained within the image. This will tell us many of your settings, which might have something to do with what you're experiencing...