What do “Yeep” and “Go yeep” mean?

Sometimes people create funny words like Yeep by analogy with other onomatopoeic terms, like peep and cheep, which are two words often used to represent the sounds made by baby birds, which can be awfully noisy and ineffectual (remember that Big Bird is an issue in this presidential campaign and that as much as they might talk and squawk, chickens have no teeth). Then there are geese, which honk, another word for beep, as in beeping one's car horn:

To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day,
To the last syllable of recorded time;
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player,
That struts and frets his hour upon the stage,
And then is heard no more. It is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.
Macbeth Act 5, scene 5, 19–28

When I was in Shanghai in 1989, I couldn't help but notice that everyone there drove with their elbows rapping out a constant tattoo on their bus, truck, and auto horns. It was a city full of sound and fury, especially after the Tien An Men Square incident.

The VP debates are usually full of sound and fury but signify nothing.

And Rory Alsop hits the nail squarely with rhymes with Veep.

I don't know whether the writer thought of all this, but it's possible. It's also one of those folk explanations for a particular behavior: one can always imagine a scenario to explain anything, even if it's wrong.

Yeep can be found innumerable times in the book series called "guardians of ga'hoole." Yeep is refered to when an owls wings are locked at it's sides and it has lost its instinct to fly for a moment.