Powerbook screen auto-dimming?

So, Apple repaired my Powerbook, and I got it back today, only it seems to have developed a weird quirk. It randomly seems to dim the display two bars just for the heck of it whenever it feels like it. I've unchecked the option to dim the display before turning it off in Energy Saver control panel, but it still does it. Oddly enough, it'll sometimes only last a second, and turn itself back to full brightness, and other times I have to manually up the brightness again.

Does anyone know what could be causing this? Apple replaced the logic board, the DC-in/sound board, RAM, and added "new cabling" inside. I did a clean reinstall of the system immediately when I got it back, and this problem developed a few minutes after I had done that.

Any ideas?

Wait, I found that if I cover the speakers, it dims right away. I guess that's the light sensor? I've never used an Aluminum Powerbook before, so I have no experience with this sort of thing... should the screen dim when a shadow from my hand falls on the speakers? Is that too sensitive? Is there a way to change this?

Ok, wow, now the Powebook has started making this really weird static noise, and it's coming from the back, from the logic board. I don't know what's causing it, but it gets louder if I move the mouse around or do anything that makes the CPU work harder.

So... I think I'll be bringing this back to the Apple Store tomorrow.