Follow your operator's manual to change to the correct frequency. I have a good picture but the audio sounds scratchy. If the wind is affecting your dish you need to check, and correct, the way it is mounted. This is usually more of a problem with roof mounted dishes. In the case of rain, all you can do is wait out the storm.
Larger dishes are less susceptible to rain fade.
The video and audio frequency should always be set precisely. I have a good picture, but it keeps fading in and out. You should check for these conditions before your program begins. This problem shows up most often when your system has been moved to a new location, or when it has come back from the repair shop. Usually it is caused by incorrect or loose wiring on the back of the receiver.