Quote from: Gandalf
Perhaps it is the scene of an extreme emotional incident, like a murder, suicide etc that sometimes actually *causes* this altered magnetic field..
you then have a resulting 'haunted location'
Doug
Although I never found any mention of emotions (and deaths) causing changes in magnetic fields in surroundings, the reverse is possible. That is, magnetic fields(especially the low frequency one's) can cause certain weired effects. Pl check this link -
http://www.erowid.org/spirit/devices/devices_article1.shtml
A quote from
http://www.borderlands.com/archives/arch/elf.htm
QuoteSubjects verbatim reports were quite revealing. (Keep in mind that none of the subjects actually said they felt the ELFs.) The most common verbatim reports occurred between 8.6 and 9.6 Hertz. Common statements were subtle "tingling" sensations in the fingers, arms, legs, teeth, and roof of the mouth. Two subjects reported a "metallic" feeling in their mouth. One subject reported a "tightness" in the chest and another subject reported a "tightness" in the stomach. Several subjects also reported sensations when the ELF frequency was between 6 and 7 Hertz. The verbatim responses in this range were "ringing" in the ears, "flushed" face, "fatigued", "tightening" in the chest and "increasing" pulse.
Sounds familiar ?

The brain operates through chemicals, electric and magnetic forces. These are the (known)media through which information flows, so it is only natural that when you mess with any of these, brain *malfunctions*.
I'm not qualified to say about the 'astral' part, but ghosts do look like entirely subjective phenomena, irrespective of causes. There is a twist, btw, some people have witnessed objects moving around, but I feel that is entirely different phenomena, and is commonly mistaken for the objective presence of a ghost.