It's been stated in the comics that Magneto gets his energy from the Earth's magnetic field; still unrealistic, but at least he doesn't lose body fat over it.
The X-Men make a last food stand: rough estimate of the calories Magneto had to consume to fuel the magnetic fields that moved the Golden Gate Bridge? 4.8 million
As for the "noise in space" thing, that's been done to death. It's just for entertainment purposes, folks. If it bothers you that much, cover your ears. Or don't watch the movie.
STARGAZING: All I see are the lights of a billion places I'll never go. --Howard Tayler, Schlock Mercenary