Is the noise reduction option switched on ?  Find it buried deep in menu the menu somewhere as a shooting parameter.

You will know if it is straight away because the camera will take as long to process the image as the exposure time. ie if the exposure was 30 secs then in camera processing will take 30 secs for each shot. Same applies to the G5.

What the camera is doing is taking a second exposure without opening the shutter therefore getting a black image with only noise on it. This it then blends with the first image in difference mode. Voila you have an image with a lot less noise.

HTH 

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html