I find it that when the lighting is not good then the photo gets noisy. How I approach Hawks is that when I see them I will not stop right away but just keep going past and then turn around a little ways away and approach slow, then gradually slow down and gently stop. Also will either get a shot out the window or get out of the vehicle slowly without banging or shutting the door. Hawks don't like it when you stop fast or make loud sudden noises.
I drove a good mile past the first pair I stopped to shoot. Never got close enough to get anything. The pair I did get to capture, I stopped as soon as I could get 80,000 lbs stopped safely, then pretty much did exactly what you do. I got out of my truck, zoomed in as far as I could and took a couple shots, then I'd move a little closer, take a few, and repeat till they started getting spooked. Then I just stood there till they settled down a bit. But at that point, I couldn't ever get closer, so I took shots where I was. I love the composition of the shot I posted, just hated the noise and slight out of focus. I know I need a better lens, but I also think part of it is the camera. Both of those will be remedied by the first of the year.