I wonder what the "guaranteed" fluctuation in the output is: what does the datasheet say?
It's ages since I 'scoped the output of a servo line, but I don't recall seeing it move much. I'll dig my scope out and have a look.
The range of a servo is from 1000 to 2000 us for 0 to 180 degrees. That's 1000/180 = 5us/degree. So if your signal's changing by 5us as shown on your scope, how can that possibly mean "shake the position a few degree"; it will at most be 1 degree of movement, unless of course the servo's badly made.
As a matter of interest, and here I'm wondering if it's a power related thing, does the scope show the same fluctuation with the servo completely out of the circuit, including power and ground?