To see and hear rain falling symbolises forgiveness and grace. Falling rain is also a metaphor for tears, crying and sadness. Alternatively, rain symbolises fertility and renewal. If you get wet from the rain, then it indicates cleaning from your troubles and problems. In particular, dreaming of acid rain indicates that you have been mislead. You are letting hatred and revenge take over and define you.
To dream that you are watching the rain from a window indicates that spiritual ideas and insights are being brought to your awareness. It may also symbolise fortune and love.
To hear rain tapping on the roof denotes spiritual ideas coming to fruition in your mind.