Has anyone experienced 'random flickering' of their strips?
I doubt there's anyone with a project larger than 50+ LEDs who hasn't
Your most likely culprit in this case is too large a resistor value. For cat5 of 18ft or less, you should need a resistor between 70-100 ohm. 220 is overkill and will round off the signal just enough to look like the occasional timing glitch (periodic flashes on a subsection of the strip). I chronicled some of my own findings on the matter here.