I'm pretty certain now, that my squeaking noise came from the speedo itself, or that location anyway. Prior to disassembly, I was able to grab the back near the speedometer and kind of move it up and down. The noise would dissipate for a while, then come back. So I disconnected the cable from the gauge cluster and applied a dab of heavy grease on the tip of the cable as well as some lithium grease. Since then, no noise has been heard whatsoever. I'm thinking the grease managed to work itself into the gears on the speedo, but could be wrong. Maybe it's a temporary stop-fix, or maybe not. Time will tell.