"I read somewhere that it never rained before the great flood in Noah's day. Is that true?"
The notion that it hadn't rained for the ten generations between Adam and Noah comes from a literal reading of Genesis. There we read, "No plant of the field was yet in the earth . . . for the Lord God had not caused it to rain upon the earth . . . but a stream would rise from the earth, and water the whole face of the ground" (2.5-6). Between this passage and Genesis 7.12 there is no mention of rain and so some have concluded that it didn't rain during the intervening 1,597 years.
As I researched this question, it occurred to me that Genesis 2.6 could reflect the annual flooding of the Nile River (before the twentieth century Egyptian flood controls). For many millennia the Nile flooded every spring and covered the tillable land of Egypt. When the waters receded, the residual silt left on the land resulted in rich, fertile soil ready for planting. But even though it made for great soil, the annual flooding couldn't provide enough water for the needs of the crops. To compensate for the lack of rainfall, irrigation trenches were dug to channel water from the Nile to the fields of crops. Thus, at least for a very limited area, local rainfall might not have been necessary for survival.
But according to Genesis 2, the Garden of Eden was located a good bit farther north, approximately where Kuwait and Iraq are today, and though the Genesis passage might reflect what happened in Egypt, the Nile flooding wouldn't apply to Eden.
So, when did it first start to rain?
The argument that there was no rain between Genesis chapters 2 and 7 is based on silence. However, arguments from silence carry little weight since they can neither corroborate nor invalidate a premise. For instance, the fact that scripture says no plants existed because there was no rain and because there were no humans to till the ground (Genesis 2.5) doesn't mean it didn't start to rain with the advent of Adam and Eve.
The underlying problem with this whole question is that it's based on the presupposition that what Genesis 2 reports is in fact what actually happened in time and history. The difficulty is in trying to use scripture as a history/science book.
To try and understand the account of the watering of the earth in Genesis 2 as a scientific fact is to ignore the implications. For the waters of the streams to rise and "water the ground" the flood waters had to come from somewhere. The Israelite cosmology suggested the water came from Chaos, or "the deep." These waters were found below the disk-shaped earth and above the dome that separated the waters (see figure). In the great world flood story (Noah and the ark) we read that the earth was flooded when three things happened: (1) the fountains of the deep burst forth; (2) the windows of heavens were opened; and (3) it rained (Genesis 7.11-12). The Israelite understanding of the "stream that rose to water the ground" in Genesis 2.6 would be a similar phenomenon where the waters rose from beneath the earth.
The only problem with all of this is above our atmosphere we find the void of space, not the waters of chaos, and the earth isn't floating on waters that are waiting to burst forth from below.
The notion of no rain on the earth for 1,597 years in human history is based on a literal interpretation of scripture and the notion that the Bible must represent an accurate reflection of science and history. But that isn't the case. The Bible is a collection of faith stories that teach us God is love, God is trustworthy, and God seeks to be in relationship with all of us. It was never intended to be a text book on science, and to try and force the Bible to reflect scientific truths is futile.
So, did it rain before Noah's great flood experience? I expect so. And I imagine all the generations preceding Noah experienced the gentle rains of spring just as we do. And when the rains stopped and the sun beamed through broken clouds, they were grateful that God had once again watered the earth and life would go on.