I have struggled with GI flicker since I first got my AMH. Since it was only certain bulbs, I thought it was bad connections in the sockets. I replaced all of the slingshot and inlane guide sockets, but I still had flicker.
The bulbs also seemed dimmer than they should be, even knowing that it's a 5V source. This weekend, I measured the voltage, and I was only getting 4.35V to my bulbs. Considering the LEDs I'm using are designed for 6.3V, it's no surprise that they are having issues.
After some digging, I found that the transistor used to control the GI is a TIP102, and I measured a 0.72V drop across it. I decided to replace it with an IRL540, and it has definitely helped the dim lamps. It seems to be helping with the flicker as well, but it will take some time to be certain. The lamps are still only at around 5.05V, so pretty low compared to the 6.3V the bulbs are designed for.
Edit: The flicker is not gone, unfortunately. I guess that the bulbs are still shifting in the socket or something to cause intermittent connection. I squeezed them for a tight fit, and none of my other games have this problem. A problem for another day.