Hi Marcin, welcome to the site and to the Critique Gallery. I hope you will enjoy it and find it a good place to learn. We try to give advice that will help people to improve their photography – both the taking and the editing of images.
in this gallery the more information you give us as regards your photographic aims and intentions, the better. You've been veryhelpful here giving us the exposure details and what you wanted to achieve.
It also helps us if you respond to critique and indicate which ideas you find helpful. That means we can tailor advice according to your needs.
It can be difficult to show rain. If the rain is light, it's harder to show but you can't organise the weather.
A slower shutter speed is required so that the falling drops appear as streaks. That goes against the advice of faster speeds for longer lenses, so you need to ensure the camera is firmly fixed to a tripod or well supported for example by a bean bag on a wall or post.
You used 1/400 here. With the short focal lenght used here you could have used a slower speed even unsupporte. Supported, I'd start with 1/60. The gull isn't moving so you don't have to worry about subject movement blur like you would for example with the smaller birds that always are on the move.
If you can shoot against the light, the raindrops and their streaks can be picked out more easily, especially if the background is dark. It'd be ok here. so it needs a bit of planning and thought about your viewpoint. Clearly wild creatures can't be directed, but observing their favourite perches will allow you to find a good viewpoint. And gulls can be easily tempted with food, so you can increase your chances of getting a shot. You may need a helper to administer the food while you wait and shoot.
This picture doesn't look particulalrly noisy, but often resizing an image to smaller dimensions reduced the appearance of noise. It may be more visibnle on the full size original.
However, this image is underexposed. Take a look at the histogram. Most tones are toward the left side and there are no lighter tones - the graph doesn't reach the far right of the Levels dialog.
It looks like the white bin has influenced the camera into giving less exposure. Trying to extract detail from such an image will increase the appearance of noise. I won't try and describe the maths and physics!
In my mod I've adjusted the Levels to get a full range of tones and brightened the image using Curves rather than Levels as I can then control contrast too and have finer control over how the lightening works.
Finally, I cropped the image so that there is more space for the bird to 'look into'. Such an off centre positioning provides a more balanced looking image too.