Mine used to flicker a lot, battery level didn't seem to matter. I could never pin down the cause, as it was noticeable but nothing I couldn't live with.
After the OTA update sent me into a boot loop and I had to flash the stock ROM I found on this forum, the flicker is completely gone. I haven't had to download any of the Virgin Mobile stuff, either. My network says Chameleon, I get the stock LG boot and shutdown animations, but everything works as it should. I still don't know what was causing the flicker, but I thought it was pretty weird that the stock ROM fixed it.