Is there a ground-loop problem if I power the sumo with one source and
the servos with another, especially if the sources are different?

Also, what are the power requirements for the sumo? I have a 7.2V
2000mah battery. But when I power the thing up, I get the low tone
buzzer sound from the sumo. I can't download any files. It just sets
there. But when I power the thing up with a bigger source, the LCD is
brite and begins accepting programs and functions properly.

Has anyone experience this, espcially the 'low' buzzer sound?