I currently use an SM57 dynamic mic in my hobby studio and have problems with electro-magnetic fields resulting in an audible hum at higher gain levels. I'm wondering if condenser microphones are less susceptible to electro-magnetic fields.
In general, the answer is yes. This does assume that the condensor mic circuitry is properly shielded in a metal handle. The SM57 is susceptible to hum fields because the grill surrounding the voice coil is plastic. The Beta 57 would be a better choice than the SM57 because of its metal grill.
It is the voice coil of the SM57 (or any dynamic mic) that "picks up" the hum field.