Originally posted by dyno I wonder if this is normal to have so much noise at 400 ISO or it's just my camera's problem. I'm not even sure this is noise or not.
The first things I'd look at is whether or not the images are properly exposed. Because it will be huge factor in noise performance.
Having said that, I know the blue channel(ie. sky) is notorious for noise and so I think it helps to be aware of that.
And finally, on the issue of what you can do other than Photoshop, I'd highly recommend shooting in RAW and using one of the advanced RAW developer softwares out there such as; Raw Therapee, which has very good Noise Reduction capabilities and is completely free. However, if you can afford it, I would highly recommend looking at Lightroom or Photoshop as they both offer exquisite Noise Reduction processing(usually fully automated) and are imo. worth every penny.
Hope this helps.
PS. Don't underestimate the value of monochromatic noise(grain) in images.