A post by Dave Johnson I grabbed from another forum.
Electrical Interference
First Texas Products & Fisher Labs August 2009
Because of the high sensitivity of modern metal detectors coupled with the proliferation of sources of electromagnetic interference, you are likely to encounter electrical interference at times during the use of your metal detector. It is important that you recognize electrical interference when present, and take appropriate measures to deal with it. This will prevent you from giving up on a worthwhile site unnecessarily, or from sending in for a repair a machine which is working properly.
Symptoms of electrical interference
Electrical interference can cause a metal detector to
Electrical Interference
First Texas Products & Fisher Labs August 2009
Because of the high sensitivity of modern metal detectors coupled with the proliferation of sources of electromagnetic interference, you are likely to encounter electrical interference at times during the use of your metal detector. It is important that you recognize electrical interference when present, and take appropriate measures to deal with it. This will prevent you from giving up on a worthwhile site unnecessarily, or from sending in for a repair a machine which is working properly.
Symptoms of electrical interference
Electrical interference can cause a metal detector to