SB,

Hawks are very teritorial, and he's attempting to scare your plane away. When it doesn't work, after a few attepmts he will leave. If you want to have some real fun, try to sucker him into following your plane through a few turns. If he does, drop the nose into a shallow dive, if he follows, pull full up and do a loop. He can't, and the Hawks reaction can be quite comical.
If you have vultures in your area, they are not teritorial, and I have flown with upwards of a dozen at a time, and even had mild collisions with them. They do not seem to be spooked at all by a glider's presence. I have enjoyed many hours of flying with Hawks and Vultures, it is very enjoyable.
I share your enthusiasm for exploring how far out you can go and still find lift. We have a slope not far from here that you can drive to top of(very convenient) and you fly out over a lake. When the wind is right, the distance out over the water you can fly and still get back is almost unbelieveable. It really is as you say, "a buzz".

Happy soaring,

David Layne