Add noise to gradient photoshop

The opacity is a multiplier. Assume:

• Layer 1 opacity = 50%
• Layer 2 opacity = 50%
• Layer 3 opacity = 50%

Net opacity = Layer1 + (Layer2 * Layer1) + (Layer3 * Layer2 * Layer1)

Or, 50% + 25% + 12.5%. You would mathematically never get to 100%.

It is possible using Animation (Timeline in CS6!) and keyframes.

1. Set your gradient overlay to its starting position.
2. Open the Animation window (Window → Animation), and expand the layer you have the gradient overlay on. Click on "style"
3. Position the animation cursor to the first frame, then place a keyframe (yellow rhombus)
4. Move the animation cursor to the last frame, place another keyframe
5. Staying on the last frame, move the gradient overlay to its desired end position.

I hope this explains it well enough, if not, I can upload an example PSD file.

(PS: I realize this question was posted 4 months ago, but others might benefit from this answer)