Also seems to be lamp/projector dependent. I had a 30ES that flickered right out of the box in low-lamp mode. Switching it to high and back to low would fix it, until the next time the projector was turned on, or the time after that. Was a minor nuisance. My 50ES has 140 hours on it right now, and hasn't flickered even once, and I've used it on low-lamp mode exclusively (except for one or two 3D movies where it auto-switches to high lamp).
Sounds like you're running high-lamp the whole time? If you received a second lamp with your projector as many of us did, it might be worth swapping out the lamp, at least temporarily. Then you'd know if it's the lamp or the projector itself..