Quoted from wrd1972_PinDoc:

Glad i found this thread. My Grand Lizard has the screeching sound in attract mode that is completely in sync with the playfield insert lights, when they are wiping back and forth. Cant really hear it during play.
All of the screws in the boards are present. I will try cleaning the pads on the boards like vid suggested, and i will try to float the sound board too.
There is a 3 wire cable running from the bottom right of the MPU to the sound card that influences the sound. If that cable gets near the speaker or any transistors, the sound gets much louder.
Will work on it some more tomorrow.

Quoted from wrd1972_PinDoc:

Okay I "floated the board, and that created a very loud humming noise, in addition to the screeching sound. Obviously a step back, so the board got reattached.
There is a cable that runs from J16 on the main board, to J1 on the soundboard, and it plays a major roll in the volume of the screeching sound I am hearing. Again the screeching is only noticeable in attract mode as the playfield lights are wiping back and forth. It is also louder when the majority of those lights are lit.
So when this cable is moved near the speaker, or the transistors on the main board, the screeching gets much louder. So what I have done is strategically routed the cable across the main board in a manner that results in the lowest volume of screeching. So I can still hear it in attract mode, but its as quiet as I can get. I am wondering if that cable were to be lengthened, and routed in a way so it does not cross the main board, would that further reduce the volume of the screeching. If I get any time, I might try this. But thats where it stands.