Here's a little tip:
another way to loop the Noise, is to Add Keyframes to the beginning and the end, and change the Blend Type in the Modifier from 'Replace' to 'Add'.
Then you can simply move one of the Keys up or down in the Graph Editor.
If you do this before toning down the Strength completely and look at the Valuesd in the N-Panel (also using the Offset, if necessary), you can get pretty exact rather easily.
