can I open up the dock myself and see what's wrong - if not fix it - without voiding the warranty?

No. If you want to avoid voiding the warranty, you have to send it in.

If I recall correctly, in the U.S., the units have only 90 days' warranty. So if the light problem is merely an annoyance, I'd just leave it until the 90 days were up and then dig in myself. Of course, that only counts if you're good with electronics and SMT soldering...

I agree that your description makes it sound like a loose solder joint somewhere. Or perhaps one of the components on the bottom of the PCB is protruding too much and coming in contact with the metal base plate. If that's the case, the only thing that could make it worse is if other solder joints came loose, and it affected other components. If that happens within the 90 days, then you can send it in.