Here's a YouTube video with the sound. Unfortunately, the sound is so deep that most microphones won't pick it up, and most computer speakers won't play it. I can't hear the sound using my usual computer speakers, but put on the ear buds or earphones, and you will hear it.
The sound is so common in the Sierra, but many people don't realize it is this bird. I have some friends who were hiking the Pohono trail in Yosemite -- it starts at the Tunnel View parking lot. They started up the trail, and then heard the sounds of that bird. They were just sure it was a bear making some sort of warning sounds, so they turned back and hurried back to the car. It ended their hike!!!
This is the best video I could find of the sound, but it doesn't sound nearly as loud here -- even with headphones -- as it does on the trail. This is how the male appears. The female is all speckled and gray -- camouflaged.
The pics below are mine. (click for larger view). This one was shadowing/harassing a hen in the trees and bushes at the base of the Half Dome subdome area. As he chased her (walking slowly), he was hissing.
This on the shortcut trail to lower Cathedral Lake:
