"sweet rain" is correct and usable in written English.
You can use it when you are describing a pleasant rain—for example, "The sweet rain made the garden smell of spring."
Unmoving heat and then a sweet soaking rain (last summer)?
So, at last, the oppressive humidity of EastEnders' Baby Swap story has broken, washing the streets of Walford in the sweet, cool rain of confession.
"Sweet September Rain" happened when the Transfer was working on The Chick Corea Songbook because Bob Belden was initially involved in that, and because he knew I was a fan of his, he would send me his own music occasionally and this was one of the pieces he sent me, which was from a move called Three Days Of Rain, and this was the theme.
There is a potted lyrical quality to the text that, marshaled in the service of an Irishy irony, brings to mind Flann O'Brien: "The boring old summer holidays were finally over, and the dull damp autumn had arrived at last, bringing with it that sweet-smelling slanty rain, enchanting early evenings and endless darkness".
One after another, they struck, and they struck, and they struck again, with all the might in their little arms, until the ghastly green monster burst apart at the seams and the sweet candy rained into their hands.
As the squirrels and farmers harvest to eat today and preserve for tomorrow, so plants and trees withdraw their energy into their roots to await the time when the soil will again be warmed by the sun and sweet spring rains.
A voice-over occasionally intones non sequiturs like "Nothing was as sweet as the rain on your lips".
But, oh -- The possibility of lightning, like a crack in the purple-black sky, the sweet chances of rain!
