I don't know why her voice was metallic sounding. Perhaps it was because it was coming from the other side. I've read that those on the other side have a hard time getting through all the atmospheric layers to make themselves heard. That said, one day a few years ago, I was sitting at the computer, not even thinking about my mother, when I clearly heard her call out my name. At the time, I wondered why she called out to me. I got my answer a couple of days later. Without going into detail, we discovered that our daughter, instead of going to classes at college, was partying. I think my mother was trying to tell me that.

In your case, I think that your mother was trying to let you know that she was ok on the other side. Or if you had spoken out loud to her after she passed, she may have called out to you to let you know she heard you.