Without the logic board connected, it will do that I've found.
I had an analog board that I tried rebuilding, and it just wouldn't work (kept making that sound). So, on a whim, I decided to try hooking it up to a logic board ("what did I have to lose?" I thought to myself). To my amazement, it worked perfectly!
As for the brightness problem, try resoldering the connections at the brightness pot. It sounds like there might be a loose connection there.
If that doesn't work, there might be a flaky resistor in that circuit (I forget what Larry Pina's book says past that).
c