Printing Photos of Aurora Borealis

[amandagal]

Any tips on printing photos of the aurora? I was recently in Alaska and took what I thought were good photos. I ran them through Lightroom's noise reduction, but they print grainy even in 4 by 6. I attached the little versions, the big ones are on my Flickr:
The Northern Lights - a set on Flickr

I shot in RAW with a Canon 40D, so I can go back and re-process them. Should I try a new lab or try some new post-processing? I really can't see the grain on my monitor until I zoom in big, but I know printers pick up more of that.

Any suggestions would be appreciated!